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EMBARGOED FOR RELEASE: Thursday, April 11, 2013, 11 a.m. Eastern Time
Note to journalists: Please report that this research was presented at a meeting of the American Chemical Society.
Newswise — NEW ORLEANS, April 11, 2013 — Scientists today reported a discovery that could speed an emerging effort to replace ethanol in gasoline with a substantially better fuel additive called butanol, which some experts regard as “the gasoline of the future.” Their report on this discovery, which holds potential to reduce the costs of converting ethanol factories to production of butanol, came at the 245th National Meeting & Exposition of the American Chemical Society, the world’s largest scientific society.
Duncan Wass explained that ethanol has become a leading biofuel — millions of gallons added to gasoline around the country each year — despite several disadvantages. Ethanol, for instance, has a lower energy content per gallon than gasoline, which can reduce fuel mileage. Ethanol also has a corrosive effect on car engines and can’t easily be used in amounts higher than 10-15 percent.
“Ethanol actually is a poor alternative fuel,” Wass said. “Butanol is much better. It contains about 30 percent more energy per gallon than ethanol, is easier to handle and more of it can be blended into each gallon of gasoline. In fact, you could fuel a car on pure butanol and it would run absolutely fine. That’s the basis for butanol’s emerging reputation as ‘the gasoline of the future.’”
Efforts already have begun to convert some ethanol factories in the Corn Belt to production of butanol, Wass explained. Those factories currently process corn into alcohol with the same fermentation technology used to make beer and beverage alcohol. Converting those factories to ferment corn into butanol would require costly modifications, estimated at $10 million-$15 million for a typical plant.
Wass and his group at the University of Bristol in the U.K. are reporting the discovery of a new family of catalysts that could enable those factories to continue producing ethanol, with the ethanol then converted into butanol. With the catalysts, ethanol factories would require less retrofitting to produce butanol. Catalysts speed up chemical reactions by lowering the amount of energy needed need to jumpstart reactions. They enable production of hundreds of everyday products, and many of the proteins that sustain life are catalysts called enzymes.
Their report was part of a symposium on renewable fuels and catalysts. Abstracts of other presentations appear below.
“These new catalysts are much better than any previously in existence,” Wass said. “There’s a long way to go before they are commercialized, but we are reporting a fundamental advance in that direction. Quite simply, they are the world’s best catalysts for making the gasoline of the future.”
The new catalysts are more selective, solving a difficult problem in which current catalysts churn out butanol as well as unwanted products. Wass said the new catalysts yield 95 percent butanol out of the total products from each batch in laboratory-scale tests.
Wass’ team acknowledges funding from BP.
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Abstracts
Catalytic conversion of ethanol to an advanced biofuel: Unprecedented selectivity to n-butanol
Butanol has emerged as the front-running sustainable liquid fuel replacement for gasoline. The development of biosynthetic pathways for its synthesis have dominated recent research but these are still challenged by very low conversion and modest selectivity. An attractive alternative is catalytically upgrading more readily available (bio) ethanol is attractive but this is hampered by modest selectivity in most cases.
This paper will report homogeneous ruthenium diphosphine catalysts for the upgrade of ethanol to butanol which show selectivity to n-butanol of over 95% at good conversion. Our preliminary mechanistic study into this system will be presented, which suggests high selectivity is achieved because the catalyst imparts control over acetaldehyde aldol condensation reactions, with evidence for an on-metal condensation step. The crucial role of ligand structure in this regard will be discussed.
Catalytic conversion of lignin fragments to fuels and chemicals on the bifunctional catalysts
The catalytic conversion of lignin fragments composed of one or two phenyls, such as guaiacol, eugenol, vanillin, and benzyl phenyl ether, into the saturated deoxygenated hydrocarbon fuels or chemicals was studied using bifunctional catalysts composed of transition/precious metal nanoparticles and acidic supports including mesoporous aerogels. While the hydrodeoxygenation of lignin monomer produced hydrocarbon fuels, the strategy of isomerization of lignin dimers followed by hydrodeoxygenation successfully produced the high carbon-number hydrocarbon fuels. The reaction pathways on the solid-acid-supported metal catalysts were studied to understand the roles of catalyst components and improve the catalyst design, which revealed the synergic effects of metal and acid catalysts. The effects of water on the reaction pathway were also studied in order to develop the selective reactions, which simulated the water-containing processes of biomass-to-fuel. The understanding of catalysts and their activity was supported by characterization methods, such as TEM, NH3-TPD, CO-chemisorption, XRD, and XPS.
Depolymerization and deoxygenation of lignin β-O-4 compounds with zeolites
Lignin is highly attractive feedstock for the sustainable production of fuels and chemicals. However, because lignin is a complex, ill-defined polymer comprised of many types of C-O bond linkages, the development of catalysts that depolymerize lignin by targeting the cleavage of b-O-4 bonds is greatly needed to realize its potential. We report the synthesis of hierarchical zeolites with controllable pore sizes and volumes. These catalysts have been characterized by a battery of techniques: XRD, NH3-TPD, N2 physisorption, SEM, ICP-OES, and XPS. To fundamentally understand how lignin decomposes during catalytic fast pyrolysis using these catalysts, the use of model compounds containing the β-O-4 linkage is necessary. We have synthesized well-defined molecules that model the β-O-4 linkages in lignin in order to understand these thermochemical conversions. Here, we report the effects of the lignin β-O-4 structure and catalyst properties on the formation of aromatic, deoxygenated products via catalytic fast pyrolysis.
Ru decorated graphene integrated in a micro-channel reactor for methantion
Graphene Oxide (G.O.) can provide excellent stability and surface area as a support material for catalysts. Synthesized by the modified Hummers process, this G.O. and alumina nanopowder were used as a support material for ruthenium catalyst for the conversion of carbon monoxide to methane. The surface of G.O. and G.O.-Al2O3 were first modified by means of a metal (Nickel) cation activation process and surface adsorption of anionic surfactant. The use of nickel as a nucleating center enhanced the Ru nanoparticle decoration on the G.O. Characterization techniques such as SEM, TEM verified the dispersion of the ruthenium on G.O. Elemental survey of the catalysts by XPS identified the presence of the ruthenium on the catalysts synthesized. Using the surface modification technique the poly-ol process promoted the deposition of ruthenium nanoparticles with a mean diameter of 2.7 nm. Porous aluminum foams supported the G.O-Ru catalysts, creating a hierarchical system with decided advantages of low-pressure drop, excellent flow characteristic and heat transfer properties.
Lignin derived chemicals and lignocellulosic biofuels
In order to focus project direction for developing renewable chemicals and fuels, critical chemical properties in the intermediate products have to be identified and ultimately controlled during processing. This presentation will focus on two related projects to demonstrate this point.
First, the synthesis and scale-up of lignin based chemicals for petroleum enhanced oil recovery will be discussed. This will include the process conversion of lignin in small batch reactors, catalyst screenings, and the lignin product characterization and definition. It will progress through continuous bench units, to a 600 lbs/hour process development unit where over 300,000 pounds of the lignin chemical were produced.
Second, the pyrolysis oils formed in the fast pyrolysis of biomass will be discussed and compared with the lignin chemicals described in the first project. Although pyrolysis oils also contain cellulosic and hemicellulosic compounds, the lignin chemicals determine much of the chemistry and other properties of the oil.
Direct catalytic conversion of ethanol stream into hydrocarbon blend-stock
We report ethanol transformation into a blend-stock hydrocarbon fuel through a one-step catalytic process. Deuterium labeling studies rule out ethanol conversion to ethylene as the first step in ethanol to hydrocarbon blend-stock process. Instead, hydrocarbon pool mechanism seems to dominate. Our work shows that water concentration in dilute ethanol or simulated fermentation stream has no effect on the catalyst or product distribution. The catalyst was observed to become coked after several hours. The coking time was dependent on space velocity and the catalyst could be regenerated at 450 °C in air. The blend-stock consists of a mixture of C3 – C16 hydrocarbons containing paraffin, iso-parrafins, olefins, and aromatic compounds with a calculated motor octane number of 95. Fractional collection of the fuel product allows for the different fractions to be used as blend-stock for gasoline, diesel, or jet fuel. Successful engine experiments were performed on a variable valve actuation gasoline engine showing comparable performance and emission data to certification gasoline.
Comparative DFT study of acetaldehyde hydrodeoxygenation mechanisms on Ru and RuO2 catalysts
The hydrodeoxygenation (HDO) mechanism of acetaldehyde, a surrogate molecule for the over 400 different oxygenated species in biomass-derived pyrolysis oil, was studied over the Ru(0001) and RuO2(110) surfaces using Density Functional Theory. Under typical HDO reaction conditions, the thermodynamic phase diagram indicates that the RuO2(110) surface is partially reduced and terminated by OH-groups on the bridging O-sites. Further reduction and creation of a surface O-vacancy site are necessary to create an active site for acetaldehyde adsorption through its terminal O-atom and selective conversion to ethylene. In contrast, acetaldehyde is easily activated on Ru(0001), but metallic Ru favors C-C bond over C-O bond scission which leads to the unwanted formation of CO and CH4. A more detailed understanding of activity and selectivity differences between metal and metal-oxide catalysts for HDO is necessary for the development of new and efficient catalysts that can lead to an increased utilization of biofuels.
Fast and selective sugar conversion to alkyl lactates and lactic acid with Sn-based bifunctional carbon silica hybrid catalysts
The synthesis of alkyl lactates or lactic acid from sugars is an important biomass route towards valuable industrial products. Short chain alkyl lactates are considered green solvents, and long chain esters are used in health care and cosmetics. Lactic acid itself is a building block for polyesters and a platform chemical. The current synthesis of lactic acid via fermentation however is energy and time consuming and one ton of gypsum byproduct is formed for every ton of lactic acid. We here report a green chemocatalytic route for the production of lactic acid and its esters direct from common sugars based on a new class of carbon-silica composite (CSM) catalysts with tunable bimodal porosity. This value-added biomass conversion requires multiple catalytic functions and ideally demonstrates the versatility and tunability of this new class of composite materials[1].
[1] de Clippel F., Dusselier, M. et al. JACS, 2012, 134 (24), pp 10089–10101
From cellulose to a potential substitute for bisphenol A: The design, application, and mechanistic understanding of a hyperbranched catalytic approach
Diphenolic acid (DPA), produced from cellulose-derived levulinic acid (LA), can potentially displace bisphenol A as a structural analogue in the preparation of polybenzoxazines, aromatic polyesters and polycarbonates.
We present the use of water-soluble sulfonated hyperbranched poly(arylene oxindole)s in combination with ultrafiltration as a conceptually novel approach for the catalytic production of LA from cellulose. LA can be subsequently converted into DPA by a thiol-promoted acid-catalyzed condensation with phenol. For this reaction, we will discuss a mechanistic study of the kinetic and regiochemical effects that alkyl- and benzyl-substituted thiols have on the observed reaction rates and product selectivity. Taft linear free energy relationships show that steric effects play a predominant role in determining the condensation rate, while kinetic effects alter the regioselectivity towards the desired p,p'-DPA isomer. The hitherto overlooked catalytic isomerization of p,p'-DPA will be demonstrated by condensation reactions with both m-cresol and 13C-labeled phenol supported by DFT calculations.
Stability of amorphous silica alumina in hot liquid water
The limited hydrothermal stability of many oxide catalysts and supports is a major bottleneck for the development of efficient processes for the conversion of biorenewable feedstocks in aqueous phase. While pure silica and alumina undergo dramatic transformations, a much higher stability is observed for amorphous silica-aluminas (ASAs) in liquid water at 200 °C. The synthesis procedure plays a major role. ASAs prepared by cogelation lose their micropore structure due to hydrolysis of siloxane bonds, but the resulting mesoporous materials still have considerable surface areas. ASAs prepared by deposition precipitation contain a silicon-rich core and an aluminum-rich shell. In hot liquid water the latter is transformed into a layer of amorphous boehmite, which protects the particle from further hydrolysis. The surface area increases slightly in the process. Independent of the synthesis methods the ASAs retained considerable concentration of acid sites. Applications for acid catalyzed reactions will be discussed.
Continuous D-Fructose dehydration to 5-hydroxymethylfurufal under mild conditions
Within the context of future biorefineries, sugars are a readily available feedstock from biomass. The selective dehydration of glucose and fructose to 5-hydroxymethylfurfural (HMF) has gained considerable attention in recent years as a possible key-step in the manufacturing of renewable chemicals and fuels.
The dehydration of D-fructose to HMF using the commercially available solid acid catalyst Amberlyst-15 (4.7 mmol H+ g-1) was investigated under batch and continuous flow conditions on a millimeter scale in 1,4-dioxane in the presence of small amounts of DMSO. Using the low boiling solvent 1,4-dioxane has several advantages over other organic solvent like the increased solubility of sugars or the lower downstream separation costs due to its high volatility. Not only the space-time-yield of the system in the flow reactor was 80 times higher than the in the conventional batch reactor but also the conversion of D-fructose (98 %) and the yield (91 %) of HMF were strongly increased under mild conditions (110 °C) and short reaction times (3 minutes). Internal and external mass transfer limitations could be identified in the continuous system. Therefore the reaction conditions were chosen in a way that the dehydration of fructose was the rate limiting step. In the long-term catalyst stability study the solvent was distilled off twice after 24 hours on stream and recycled bringing the overall reaction time to 72 hours with only small losses of 0.5-1 % in the yield of HMF. This small decrease could be explained by the water that accumulated in the system due to the recycling of the solvent increasing the rate of rehydration to levulinic acid.
reference Continuous D-Fructose Dehydration to 5-Hydroxymethylfurfual Under Mild Conditions C. Aellig, I. Hermans, ChemSusChem 2012 , 5, 1737-1742.
Deconstruction of lignin model compounds and biomass-derived lignin using layered double hydroxide catalysts
Lignin is an underutilized value stream in current biomass conversion technologies because there exist no economic and technically feasible routes for lignin depolymerization and upgrading. Base-catalyzed deconstruction (BCD) has been applied for lignin depolymerization (e.g., the Kraft process) in the pulp and paper industry for more than a century using aqueous-phase media. However, these efforts require treatment to neutralize the resulting streams, which adds significantly to the cost of lignin deconstruction. To circumvent the need for downstream treatment, here we report recent advances in the synthesis of layered double hydroxide and metal oxide catalysts to be applied to the BCD of lignin. These catalysts may prove more cost-effective than liquid-phase, non-recyclable base, and their use obviates downstream processing steps such as neutralization. Synthetic procedures for various transition-metal containing catalysts, detailed kinetics measurements using lignin model compounds, and results of the application of these catalysts to biomass-derived lignin will be presented.
Reforming or defunctionalization of alcohols: A computational study
Reactions of 1- and 2-propanol, which are observed in the context of aqueous phase processes over platinum, were explored at the DFT-GGA level. We examined reaction pathways for forming H2 (and ethane) or alkanes (propane). We found hydrogen formation favored over alkane formation, in agreement with experiment. In the formation of H2, we focused on the dissimilar behavior of primary and secondary alcohols. The CO2 produced can be directly released or formed after decarbonylation, in a subsequent water-gas shift reaction. Our calculations show that the species undergoing C-C bond cleavage depends on the nature of the catalyst surface, i.e. the size of facets vs. the density of surface defects. Various pathways, involving the cleavage of the alcohol C-O bond, seem feasible for forming alkanes. A dehydration-hydrogenation mechanism, via propylene as intermediate, is preferred in our model study.
Catalytic reaction on FeN4/C site of nitrogen functionalized carbon nanotubes as cathode catalyst for hydrogen fuel cells
In this work, we utilized first-principles spin-polarized DFT calculations to study the catalytic reaction steps on FeN4/C site of N-CNTs for ORR. The results show that O2 can be adsorbed and partially reduced on FeN4 site without any activation barrier. The reduced O2 can further react with H+ and e- through a direct pathway, completing the water formation reaction (WFR), without any activation energy barrier. Through an indirect pathway, the WFR process is completed with a small activation barrier (0~0.16 eV) via transition state (TS). From intermediate states to TS, H+ can obtain a kinetic energy of about 1.57 eV, due to the Coulomb electric interaction, and easily overcome the activation energy barrier during WFR process. We further simulated the attacking processes of H2PO4- and SO42- to the FeN4/C site of N-CNTs. The results show that Fe atom cannot be removed from FeN4/C site in the acidic purification process.
Catalytic conversion of ethanol to an advanced biofuel: Exploring ligand effects
Butanol has emerged as the front-running sustainable liquid fuel replacement for gasoline. The development of biosynthetic pathways for its synthesis have dominated recent research but these are still challenged by very low conversion and modest selectivity. An attractive alternative is catalytically upgrading more readily available (bio)ethanol but this is hampered by modest selectivity in most cases. Recently we reported homogeneous ruthenium diphosphine catalysts for the upgrade of ethanol to butanol which show unprecedented selectivity to n-butanol at good conversion. This paper will report alternative ruthenium catalysts utilising a variety of supporting ligand structures and how these effect reaction selectivity and conversion.
Transesterification of canola oil to biodiesel using high surface area calcium oxide
Calcium oxide (CaO) is a promising heterogeneous catalyst for transesterification of triglycerides to fatty acid methyl esters (FAME). Various sources of CaO (calcium acetate, calcium carbonate, calcium hydroxide, and calcium oxalate) have been extensively studied [1]. Results have shown that the catalytic activity is largely dependent on the source. It is proposed that the surface area of the obtained CaO (ranged from 10- 25m2/g) plays a major role in the conversion. In this study, a CaO with four fold surface area (110m2/g) is synthesized by modification of CaCO3with polyethylene glycol. The FAME yields from this material are compared with commercial CaO under similar conditions.
Compared with commercial CaO, FAME yields obtained using the high surface area CaO was higher by almost 10%. Results on leaching of calcium currently under study to determine the number of potential reuse cycles and results will also be presented. In addition to CaO, transesterification using bifunctional catalysts containing CaO and/or Al2O3 will also be presented.
Nanoscale strontium titanate photocatalysts for overall water splitting
SrTiO3 (STO) is a large band gap (3.2 eV) semiconductor that catalyzes the overall water splitting reaction under UV light irradiation in the presence of a NiO cocatalyst. As we show here, the reactivity persists in nanoscale particles of the material, although the process is less effective at the nanoscale. To reach these conclusions, Bulk STO, 30 ± 5 nm STO, and 6.5 ± 1 nm STO were synthesized by three different methods, their crystal structures verified with XRD and their morphology observed with HRTEM before and after NiO deposition. In connection with NiO, all samples split water into stoichiometric mixtures of H2 and O2, but the activity is decreasing from 28 -mol H2 g-1 h-1 (bulk STO), to 19.4 -mol H2 g-1 h-1 (30 nm STO), and 3.0 -mol H2 g-1 h-1 (6.5 nm STO). The reasons for this decrease are an increase of the water oxidation overpotential for the smaller particles and reduced light absorption due to a quantum size effect. Overall, these findings establish the first nanoscale titanate photocatalyst for overall water splitting.
Computational catalysis at solid-liquid interfaces for the hydrodeoxygenation of organic acids
One of the principle goals of modern catalysis research is to understand reaction mechanisms on solid surfaces to a degree that practical activity and selectivity descriptors can be identified that permit the rational design of new stable catalysts with unprecedented activity and selectivity. High selectivity towards a single reaction product is driven both by economics and the goals of green catalysis, where atom- and energy-efficient processes are required to conserve the world's limited resources.
In this paper we present a computational case study for the determination of activity and selectivity descriptors for the hydrodeoxygenation (HDO) of organic acids on transition metal surfaces in various environments. In particular, we investigated activity and selectivity issues in the decarboxylation, decarbonylation, and reductive deoxygenation of propanoic acid on Pd(111) model surfaces in vacuum, liquid water, liquid dodecane, and liquid alcohols.
Optimising the nanoporous architecture of solid acid and base catalysts for biodiesel synthesis
Dwindling oil reserves and growing concerns over CO2 emissions and associated climate change are driving the utilisation of renewable feedstocks as alternative, sustainable fuel sources. While rising oil prices are improving the commercial feasibility of biodiesel production, many current processes still employ homogeneous acid and/or base catalysts to transform plant or algae oil into the fatty acid methyl ester (FAME) components of biodiesel. Fuel purification requires energy intensive aqueous quench and neutralization steps, thus the rational design of new high activity catalysts is required to deliver biodiesel as a major player in the 21st century sustainable energy portfolio. Advances in the development of heterogeneous catalysts for biodiesel synthesis require catalysts with pore architectures designed to improve the accessibility of bulky viscous reactants typical of plant oils. Here we discuss how improvements to active site accessibility and catalyst activity in transesterification or esterification reactions can be achieved either by designing hierarchical pore networks or by pore expansion and use of interconnected pore architectures.
Cleavage of lignin model compounds by rhenium catalyzed C-O activation
Lignin is an attractive renewable carbon feedstock for the production of chemicals or fuels. β-Hydroxy aryl ethers are the most abundant functional group in Lignin's polymeric network and lignin derived crack products. Therefore, (2-phenoxy)phenylethanol compounds are widely used in model studies.
In the present work Methyltrioxorhenium as precatalyst has been investigated and applied in the homogenous cleavage of Lignin model compounds. A quantitative conversion of the model compound to phenylacetaldehyde and guaiacol can be obtained in an almost equal ratio.
Synthesis of electroless CuPd catalyst for glycerol hydrogenolysis
A CuPd/Al2O3 catalyst was prepared through electroless deposition method and its catalytic properties in the hydrogenolysis of glycerol to propylene glycol evaluated. Although Cu and Pd can be electrolessly plated singly, the co-deposition of both metals in the same (re-usable) bath has not been documented. Co-deposition was accomplished through use of various reducing and complexing agents and combinations of these agents used in electroless bath. Preliminary results demonstrate feasibility of co-depositing of Cu and Pd from the same electroless bath. Similarly, CuPd/Al2O3 catalysts were prepared through the impregnation method.
Initial glycerol hydrogenolysis was done using a batch reaction setup. Issues related to electroless bath stability, effects of temperature and reducing agent composition will be discussed. The deposited CuPd/Al2O3 catalysts are characterized using SEM, XRD, TEM and EDAX and their results will be presented. A comparison of the hydrogenolysis yield of electroless based catalyst with impregnation based catalyst will be presented.
Selective aerobic oxidation methods for lignin conversion to simple aromatic compounds
We are pursuing oxidative methods for selective, high-yield conversion of lignin into valuable small molecule products. We recently reported a catalytic method for chemoselective aerobic oxidation of diols,1 and we anticipate that similar methods could be employed to achieve selective oxidation of lignin. Our initial efforts utilize dimeric model compounds (e.g., 1 ) with a β-O-4 linkage to simulate the chemical reactivity expected from authentic samples of lignin. Diverse alcohol oxidation methods have been investigated to establish whether selective oxidation of the primary aliphatic or the secondary benzylic alcohol in 1 could be achieved. Oxidation reactions with traditional chemical oxidants show that TEMPO-based methods enable highly selective oxidation of this substrate. The selectivity for oxidation of the primary aliphatic vs. secondary benzylic alcohol is dependent upon the specific reagent/catalyst and reaction conditions. These results established useful benchmarks for the development of analogous catalytic oxidation methods that use O2as the stoichiometric oxidant. In the best case, exclusive oxidation of the benzylic alcohol is can be achieved in 96% isolated yield. Efforts associated with the development of these methods and their application to selective lignin conversion will be presented.
Acknowledgement: This work was funded by the DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science DE-FC02-07ER64494).
Reference (1) Hoover, J. M.; Stahl, S. S. J. Am. Chem. Soc. 2011 , 133, 16901-16910.
Rational design of cellulase-mimetic polymeric acid catalysts for saccharification of lignocelluloses
Hydrolysis of cellulose to glucose is the most critical step in the bioconversion of lignocellulosic materials to fuels and chemicals. To mimic cellulases in cellulose hydrolysis, a series of polymeric solid acid catalysts were synthesized using polystyrene and polyacrylic acid as backbone with halides as cellulose-binding groups and sulfonic acid as cellulose-hydrolytic groups. It was found that these synthesized catalysts could hydrolyze microcrystalline cellulose (Avicel) to glucose at a yield of approximately 50% in 5 h at 120 °C. Similar glucose yield was achieved when applied to dissolved pulp under the same conditions. When applied to real biomass agave leaf, only 12% glucose yield was achieved in 20 h at 120 °C. It was also found that the quantity of the binding domain was critical for a satisfactory catalytic performance. It seems that multiple binding domains were better than single one.
Mechanistic investigation of acid-catalyzed cleavage of aryl-ether linkages: Implications for lignin depolymerization
Carbon-oxygen bonds are the primary inter-monomer linkages lignin polymers in plant cell walls, and as such, catalyst development to cleave these linkages is of paramount importance to deconstruct biomass to its constituent monomers for the production of renewable fuels and chemicals. For many decades, acid catalysis has been used to depolymerize lignin. Lignin is a primary component of plant cell walls, which is connected primarily by aryl-ether linkages, and the mechanism of its deconstruction by acid is not well understood, likely due to its heterogeneous and complex nature compared to cellulose. For effective biomass conversion strategies, utilization of lignin is of significant relevance and as such understanding the mechanisms of catalytic lignin deconstruction to constituent monomers and oligomers is of keen interest. Here, we present a comprehensive experimental and theoretical study of the acid catalysis of a range of dimeric species exhibiting the β-O-4 linkage, the most common inter-monomer linkage in lignin. We demonstrate that the presence of a phenolic species dramatically increases the rate of cleavage in acid at 150oC. Quantum mechanical calculations on dimers with the para-hydroxyl group demonstrate that this acid-catalyzed pathway differs from the nonphenolic dimmers. Importantly, this result implies that depolymerization of native lignin in the plant cell wall will proceed via an unzipping mechanism wherein β-O-4 linkages will be cleaved from the ends of the branched, polymer chains inwards toward the center of the polymer. To test this hypothesis further, we synthesized a homopolymer of β-O-4 with a phenolic hydroxyl group, and demonstrate that it is cleaved in acid from the end containing the phenolic hydroxyl group. This result suggests that genetic modifications to lignin biosynthesis pathways in plants that will enable lower severity processes to fractionate lignin for upgrading and for easier access to the carbohydrate fraction of the plant cell wall.
Design of leach-resistant supported acid catalysts for continuous carbohydrate dehydration
Supported/solid acid catalysts are desirable for continuous (flow) processing in carbohydrate dehydration, as well as for coupling dehydration with other catalytic reactions that have different pH requirements. The widely-used and effective propylsulfonic acid catalysts supported on oxides show rapid leaching under hydrothermal, flow conditions. This deactivation pathway is only partly ameliorated by increasing the hydrophobicity of the support. By polymerizing an acid-modified reaction promoter onto the internal pore surfaces of ordered mesoporous silica, the reaction selectivity and catalyst stability can be simultaneously enhanced, for example, in the dehydration of fructose to 5-hydroxymethylfurfural.
Aqueous-phase hydrogenation of biomass-derived oxygenates over monometallic catalysts
The reaction rates for the aqueous-phase hydrogenation (APH) of acetaldehyde, propanal, acetone, xylose, furfural, and furfuryl alcohol; and the aqueous-phase hydrogenolysis of tetrahydrofurfuryl alcohol and xylitol, have been measured over alumina-supported monometallic catalysts (Pd, Pt, Ru, Rh, Ni, and Co) in a high throughput reactor. The rates of the APH of the carbonyl compounds are highly dependent on the functionality of the feed molecule and catalyst. In particular, Ru is most active for the APH of acetaldehyde, propanal, acetone, and xylose. The measured rates of APH decrease in the order of acetone; acetaldehyde and propanal; xylose; furfural; and furfuryl alcohol, and the aqueous-phase hydrogenolysis is much slower than the APH. To achieve a mechanistic understanding DFT calculations and microkinetic modeling are performed on several monometallic surfaces. Predicted and measured rates are compared to validate proposed reaction mechanisms, following which activity descriptors are identified to facilitate the formulation of new catalysts.
SUMMARY Scientists today reported a discovery that could speed an emerging effort to replace ethanol in gasoline with a substantially better fuel additive called butanol, which some experts regard as “the gasoline of the future.” Their report on discovery, which holds potential to reduce the costs of converting ethanol factories to production of butanol, came at the 245th National Meeting & Exposition of the American Chemical Society, the world’s largest scientific society.
KEYWORDS: Chemistry/Physics/Materials Sciences (Energy/Fuel (non-petroleum))Bottom of Form Bottom of Form
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