Jean Marcel R. Gallo

Conversion of Hemicellulose into Furfural Using Solid Acid Catalysts in γ‐Valerolactone

The effective conversion of lignocellulosic biomass into fuels and chemicals requires the utilization of both hemicellulose and cellulose, consisting primarily of C5 and C6 sugars, respectively. Catalytic conversion strategies for hemicellulose are of particular importance because biological conversion of C5 sugars is not as efficient as the conversion of C6 sugars. In addition, C5 sugars/oligomers are produced as a side stream in the pulp and paper industry, which provides an opportunity to create value-added products. Among the products that can be obtained from C5 sugars, furfural is a particularly promising option, as it can replace crude-oil-based organics for the production of resins, lubricants, adhesives, and plastics, as well as valuable chemicals, such as furfuryl alcohol and tetrahydrofurfuryl alcohol. Current methods for production of furfural from hemicellulose use mineral acid catalysts which are corrosive, difficult to recover from the reaction mixture, and pose environmental and health risks. Importantly, current yields for the production of furfural in water are low (e.g., < 60%). Biphasic systems improve the yield of furfural and its separation from the mineral acid, and can be employed for lignocellulosic biomass which has been pretreated with mineral acids. Ideally, it is desirable to replace mineral acids with solid acids in lignocellulose processing. However, the use of solid acid catalysts in an aqueous environment is challenging in view of catalyst degradation and/or leaching in aqueous solution at elevated temperatures (e.g., 430 K). Moreover, biphasic systems typically require the use of salts to achieve good separation of the phases and to improve the efficiency of the extracting organic layer, and solid catalysts cannot be used in this case because the exchange of protons on the catalyst with cations in solution leads to deactivation of the heterogeneous catalyst. The aforementioned difficulties associated with the conversion of xylose into furfural can be alleviated by using gvalerolactone (GVL) as a solvent in a monophasic system with solid acid catalysts. Importantly, GVL is a solvent which can be produced from lignocellulose, and Horvath and coworkers have been strong proponents for the use of GVL as a solvent in biomass processing. Using GVL as the solvent increases the rate of xylose conversion and decreases the rates of furfural degradation reactions. In addition, furfural has a higher volatility than GVL and can thus be obtained as a top product in a distillation step. Alternatively, GVL, a valuable chemical with multiple uses, can be synthesized as the end product of the process, thereby eliminating product purification steps. Furthermore, the use of a monophasic reaction system eliminates the loss of the product in the aqueous phase, the need for a liquid–liquid separation step, and reduces mixing requirements. Additionally, by minimizing the concentration of water present in the reactor, it is possible to use solid catalysts for the conversion of xylose (and xylose oligomers) into furfural with minimal degradation of the catalyst and without leaching of acid sites into solution. Figure 1 shows the furfural yields achieved, after complete xylose conversion, for different solid acid catalysts. The catalysts contained Bronsted and/or Lewis acid sites, and just GVL was used as the solvent. Even though water was not added in the reaction mixture, it is a by-product of dehydration, and its concentration can reach up to 0.7 wt% with quantitative yields of furfural. Catalysts, such as g-Al2O3 (galumina), Sn-SBA-15, and Sn-beta, which contain only Lewis acid sites, resulted in the lowest yields of furfural (see Figure S1 in the Supporting Information for FTIR measure-

Production and upgrading of 5-hydroxymethylfurfural using heterogeneous catalysts and biomass-derived solvents

High yields of HMF from glucose can be achieved using biomass-derived solvents and a combination of solid Lewis and Bronsted catalysts in a salt-free reaction system. The HMF produced in this system can be oxidized to FDCA or hydrogenated to DMF, both being high-value chemicals.

Solvent Effects in Acid-Catalyzed Biomass Conversion Reactions**

Reaction kinetics were studied to quantify the effects of polar aprotic organic solvents on the acid-catalyzed conversion of xylose into furfural. A solvent of particular importance is γ-valerolactone (GVL), which leads to significant increases in reaction rates compared to water in addition to increased product selectivity. GVL has similar effects on the kinetics for the dehydration of 1,2-propanediol to propanal and for the hydrolysis of cellobiose to glucose. Based on results obtained for homogeneous Brønsted acid catalysts that span a range of pKa values, we suggest that an aprotic organic solvent affects the reaction kinetics by changing the stabilization of the acidic proton relative to the protonated transition state. This same behavior is displayed by strong solid Brønsted acid catalysts, such as H-mordenite and H-beta.

Direct conversion of cellulose to levulinic acid and gamma-valerolactone using solid acid catalysts

Cellulose was converted with high yield (69%) to levulinic acid (LA) using Amberlyst 70 as the catalyst and using a solution of 90 wt% gamma-valerolactone (GVL) and 10 wt% water as the solvent, compared to the low yield of 20% obtained in water. The LA was upgraded to GVL without any neutralization or purification steps due to the solubilization of humins by the GVL solvent. High LA yields (54%) were also obtained from real biomass (corn stover).

Physicochemical Characterization and Surface Acid Properties of Mesoporous [Al]-SBA-15 Obtained by Direct Synthesis

In this work, [Al]-SBA-15 samples were prepared by three different direct synthesis methods and one postsynthesis procedure, aiming to study the influence of the preparation procedures on their structural, textural, and physicochemical features. To this aim, samples were investigated by combining different experimental techniques (XRD, N(2) physisorption, (27)Al-MAS NMR, and IR spectroscopy). All preparation methods led to the formation of aluminum-containing SBA-15 samples. Nevertheless, depending on the preparation procedure, samples exhibited different structural, textural, and surface characteristics, especially in terms of Brønsted and Lewis acid sites content. [Al]-SBA-15(1) was synthesized by the pH-adjusting method and presented the lowest surface area and pore volumes. Its surface displayed three families of medium and one family of high strength Brønsted acid sites. The Brønsted/Lewis ratio was 3.49. [Al]-SBA-15(2) and [Al]-SBA-15(3) were synthesized by prehydrolysis of the silica and the aluminum precursors. In [Al]-SBA-15(2), ammonium fluoride was used as silica condensation catalyst. These two materials presented similar surface area, pore diameters and volumes, and Brønsted acidity. The Brønsted/Lewis acid sites ratio were 3.07 and 2.15 for [Al]-SBA-15(2) and [Al]-SBA-15(3), respectively. The [Al]-SBA-15(P) obtained by postsynthesis alumination displayed surface area similar to that of [Al]-SBA-15(3), Brønsted/Lewis acid sites ratio of 2.75, and Brønsted acidity similar to that of [Al]-SBA-15(1). The presence of extra-framework aluminum oxide was identified only on [Al]-SBA-15(3) and [Al]-SBA-15(P).

Effects of γ-valerolactone in hydrolysis of lignocellulosic biomass to monosaccharides

The use of γ-valerolactone as solvent for acid-catalyzed biomass hydrolysis reactions increases reaction rates compared to reactions carried out in water. In addition, a low apparent activation energy for biomass hydrolysis and a higher value for monosaccharide conversion are displayed using GVL as solvent, leading to favorable energetics for monosaccharide production from biomass.

A Tailored Microenvironment for Catalytic Biomass Conversion in Inorganic–Organic Nanoreactors†

The efficient and selective conversion of biomass-derived renewable feedstocks into chemicals and fuels remains a major techno-economic challenge. Fructose, a simple carbohydrate that can be obtained from cellulose, can be dehydrated to a potential platform chemical, 5-hydroxymethylfurfural (HMF). The selectivity for HMF is a function of the fructose tautomer distribution, which varies with solvent polarity and temperature. Near-quantitative conversion of fructose into HMF has only been obtained in non-aqueous, polar aprotic solvents (such as, DMSO or NMP), or in ionic liquids. However, HMF separation from such high-boiling and/or costly solvents is energy-intensive and lowers the yield, even when combined with immiscible, low-boiling solvents. Herein, we describe an organic–inorganic nanocomposite catalyst that converts fructose selectively (> 80 %) into HMF in a flow reactor, while eliminating separation issues and the need for environmentally unfriendly solvents. We obtain the highest reported HMF yields to date in a monophasic, readily separable solvent, avoiding the undesirable use of salts. Our previous studies of fructose dehydration to HMF employed silicas and organosilicas with pore-directed alkylsulfonic acid groups as heterogeneous catalysts. Ordered mesoporous silica-based catalysts were found to be more selective and robust than catalysts with similar chemical compositions but non-ordered pores. Upon incorporating bifunctional organosilanes containing both alkylsulfonic acid groups and thioether/sulfone groups to promote fructose tautomerization to the desired furanose tautomers, we observed further, modest selectivity improvements relative to propylsulfonic acid-functionalized silicas. We hypothesized that in order to achieve HMF selectivities comparable to those reported with homogeneous systems, the microenvironment throughout the pore channels (rather than just localized near the active sites) should promote fructose tautomerization. Soluble organic polymers have been reported to act as pseudo-solvents, encapsulating reactants in a local microenvironment that can be favorably tailored for catalysis. Furthermore, the pores of acid-functionalized ordered mesoporous materials (both silicas and organosilicas) are large enough to accommodate such macromolecules. Poly(vinylpyrrolidone) (PVP), a polar aprotic polymer, was intercalated by incipient wetness impregnation into the pores of unmodified SBA-15 silica (Scheme 1), as well as into

Catalytic transformations of ethanol for biorefineries.

Brazil and the USA are the major bioethanol producers in the world, and the main application of this alcohol is as fuel. Since Brazilian ethanol is the cheapest in the world, there is a crescent interest in its use as a building block for biorefineries. Bioethanol can be used for the direct production of drop-in chemicals, such as ethylene, propylene, 1,3-butadiene and larger hydrocarbons, as well as for the production of oxygenated molecules, such as 1-butanol, ethyl acetate, acetaldehyde, and acetic acid. In this critical review, the development of heterogeneous catalysts for the conversion of ethanol into these commodity chemicals will be discussed.

Density Functional Theory and Reaction Kinetics Studies of the Water-Gas Shift Reaction on Pt-Re Catalysts

Periodic, self‐consistent density functional theory calculations (DFT‐GGA‐PW91) on Pt(1 1 1) and Pt3Re(1 1 1) surfaces, reaction kinetics measurements, and microkinetic modeling are employed to study the mechanism of the water–gas shift (WGS) reaction over Pt and Pt–Re catalysts. The values of the reaction rates and reaction orders predicted by the model are in agreement with the ones experimentally determined; the calculated apparent activation energies are matched to within 6 % of the experimental values. The primary reaction pathway is predicted to take place through adsorbed carboxyl (COOH) species, whereas formate (HCOO) is predicted to be a spectator species. We conclude that the clean Pt(1 1 1) is a good representation of the active site for the WGS reaction on Pt catalysts, whereas the active sites on the Pt–Re alloy catalyst likely contain partially oxidized metal ensembles.

High-level production and purification of biologically active proteins from bacterial and mammalian cells using the tandem pGFLEX expression system

Because of the complexities involved in the regulation of gene expression in Escherichia coli and mammalian cells, it is considered general practice to use different vectors for heterologous expression of recombinant proteins in these host systems. However, we have developed and report a shuttle vector system, pGFLEX, that provides high-level expression of recombinant glutathione S-transferase (GST) fusion proteins in E. coli and mammalian cells. pGFLEX contains the cytomegaloma virus (CMV) immediate-early promoter in tandem with the E. coli lacZpo system. The sequences involved in gene expression have been appropriately modified to enable high-level production of fusion proteins in either cell type. The pGFLEX expression system allows production of target proteins fused to either the N or C terminus of the GST pi protein and provides rapid purification of target proteins as either GST fusions or native proteins after cleavage with thrombin. The utility of this vector in identifying and purifying a component of a multi-protein complex is demonstrated with cyclin A. The pGFLEX expression system provides a singular and widely applicable tool for laboratory or industrial production of biologically active recombinant proteins in E. coli and mammalian cells.