Sulfonic Acid Sites Research Articles

Selective conversion of biomass-derived furfuryl alcohol into n-butyl levulinate over sulfonic acid functionalized TiO2 nanotubes

Sulfonic acid functionalized titanate nanotubes were prepared by the sulphonation reaction of hydrothermally synthesized TiO2 nanotubes (TNTs) using chlorosulfonic acid as the sulfating agent. The as-prepared catalysts were characterized by fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD) analysis, thermogravimetry-differential thermal gravimetry (TG-DTG) and X-ray photoelectron spectroscopy (XPS) techniques. The characterization results revealed that the catalysts retained the tubular structure of the TNTs and possessed a large number of active sulfonic acid sites. The catalytic performance of the catalysts for the synthesis of n-butyl levulinate was investigated via the alcoholysis of biomass-derived furfuryl alcohol under atmospheric pressure. The effects of the reaction factors such as the catalyst dosage, reaction time, and temperature on the alcoholysis of the furfuryl alcohol were systematically studied. Under mild conditions, about 79.9% yield of n-butyl levulinate was achieved. In addition, the catalysts showed a stable catalytic performance after four consecutive cycles. Furthermore, no leaching of the active species was observed during the hot filtration testing, which can be attributed to the covalently linked –SO3H groups on the TNTs surface. In addition, the opened tubular nanostructure of the catalyst and the introduced strong Brønsted acid sites exhibited synergistic effects, which facilitated the selective conversion of the furfuryl alcohol to butyl levulinate.

Solid acid catalysts based on sulfonated carbon nanostructures embedded in an amorphous matrix produced from bio-oil: esterification of oleic acid with methanol

In this work, a solid acid catalyst based on different nanostructures, e.g. graphene, nanotube, nano-onions, nanographite, embedded in amorphous carbon matrix was used as a catalyst on esterification reaction of oleic acid and methanol. The materials were characterized by transmission electron microscopy, elemental analysis, thermogravimetric analysis coupled with mass spectrometry, surface area analyses and potentiometric titration showing the presence of sulfonic acid sites (0.02-0.30 mmol g−1) on the carbon structures. The obtained materials were used as catalysts for the esterification of oleic acid with methanol (1:10 M ratio) showing conversions of 95 %, using 2.5 wt % at 100 °C for 3 h. Reuse reactions showed that catalytic activity decreased to 20% after 4 uses, probably due to leaching or methylation of sulfonic groups. Activation energy of the esterification reaction was also calculated, e.g. 52 kJ mol−1.

Propyl-SO3H functionalized graphene oxide as multipurpose solid acid catalyst for biodiesel synthesis and acid-catalyzed esterification and acetalization reactions

A graphene based acid catalyst, GO-PrSO3H, was prepared through a simple two-step process. Surface modification with (3-mercaptopropyl) trimethoxysilane followed by oxidation of sulfide groups led to the production of sulfonic acid sites on graphene oxide nanosheets. The results of various physicochemical techniques approved the synthesis of desired catalyst. The amount of acid sites was measured via the acid-base treatment with triethylamine which exhibited 1.07 mmol/g H+ in the catalyst structure. Two kinds of acid-catalyzed reactions i.e. esterification and acetalization were adopted to evaluate the catalytic performance of prepared catalyst. More than 90% conversion was achieved for butyl acetate production in acetic acid esterification with n-butanol. Moreover, methyl oleate as one of the main components of biodiesel was produced with good yield over the prepared catalyst via oleic acid esterification with methanol. The 1H NMR technique was also conducted to characterize and determine the amount of produced methyl oleate. Finally, the benzaldehyde acetalization with ethylene glycol was performed which high conversion (92%) was obtained at 3 h. The catalyst reusability for both esterification and acetalization reactions demonstrated the catalyst stability after five reaction cycles.

Catalytic Applications of Large Pore Sulfonic Acid-Functionalized SBA-15 Mesoporous Silica for Esterification

Abstract We report the preparation of pore expanded and sulfonic acid functionalized mesoporous silica catalysts by using different kinds of swelling agents such as 1,3,5-trimethyl benzene (TMB), n-decane (D), n-tridecane (TD), and n-hexadecane (HD) at two different ratios of swelling agent/surfactant. Non-swelled mesoporous silica catalyst, SBA-15-SO3H, was also prepared for comparison. The performance of the sulfonic acid functionalized solid acid catalysts by using one-pot synthesis procedure was evaluated in terms of their catalytic activity in the esterification of propionic acid with methanol. The catalysts have been characterized by X-ray diffraction to investigate the phase transition between the hexagonally packed arrangement of cylindrical pores and mesocellular silica foams (MCF), and N2 adsorption/desorption technique in terms of pore size and distributions. It was concluded from the XRD and N2 adsorption/desorption analyses that hexagonally packed and cylindrical pore structure is maintained only for low ratio of swelling agent/surfactant and the increase of the dimension of a template micelle is accompanied by an increase in structural disruption, which was attributed to the phase transition from highly ordered hexagonal arrangement to mesocellular foam (MCF) phase with large nodded pore structures rather than cylindrical pores. Among the different swelling agents, TMB and D were found to be effective for the increase in pore diameter (up to 8 and 7.8 nm), whereas, TD and HD (6.6 nm) are effective to maintain the ordered X-ray diffraction patterns resulting mesoporous materials without giving enlargement of pore diameter in comparison with TMB and D. Pore expanded catalysts, SBA-15-SO3H-TMB-0.1 and SBA-15-SO3H-D-0.1, exhibit 68 and 43% enhancement in turnover frequency toward propionic acid methanol esterification, respectively, over non-swelled SBA-15-SO3H, despite possessing similar acid strengths. The increased activity especially for SBA-15-SO3H-TMB-0.1 and SBA-15-SO3H-D-0.1 likely reflects the accessibility to the active sulfonic acid sites as well as acidity.

Etherification of 5‐Hydroxymethylfurfural to Biofuel Additive Catalyzed by Aquivion® PFSA Modified Mesoporous Silica

Catalytic etherification of 5‐hydroxymethylfurfural (HMF) with isobutene (IB) to a biodiesel additive, that is, 5‐(tert‐butoxymethyl)‐furfural (tBMF), is studied on the Aquivion® perfluorosulfonic acid resin (PFSA) modified mesoporous silica (Aquivion®/m‐SiO2) solid acid. Mesoporous silica, composed of amorphous silica‐particle aggregates, is synthesized by the sol–gel method using the amphiphilic Aquivion® PFSA as both the acidic and the template reagent. The silica surface is then modified by the Aquivion® resin, leading to the hybrid Aquivion®/m‐SiO2 solid acid bearing highly accessible sulfonic acid sites and adequate porous structure. The catalytic properties, including composition, thermal stability, acidity, porosity, and morphology, are characterized by FTIR spectroscopy, Raman spectroscopy, solid‐state NMR spectroscopy, XPS, TGA/DTG, elemental analysis, potentiometric titration, N2 physisorption, SEM, and TEM. The influence of different reaction parameters, such as catalyst dosage, reaction time and temperature, reactants composition, and solvent, is investigated. The optimal Aquivion®/m‐SiO2 catalyst (10 wt.‐%), with an accessible acidity of 45 µmolH+ gcatal.–1 demonstrates 78 % conversion of HMF and 66 % yield of tBMF, in the presence of THF, after 3 h at 90 °C, whereas the yield of byproduct 5,5′‐[oxy‐bis(methylene)]bis‐2‐furfural (OBMF), generated by the oligomerization of HMF, is lowered to 4 %. The developed catalyst demonstrates good stability after regeneration for five consecutive cycles.

Organic–Inorganic Composites Based on Gel-Type Sulfonic Resin KU-2-8 and Zirconia: Acid and Catalytic Properties in the Etherification Reaction of iso-Butylene with Ethanol

Although acid and catalytic properties of the sulfonic resins and zirconia are well-characterized, a little is known about their composites, particularly about the KU-2-8-ZrO2 composites, in which KU-2-8 is a commercial gel-type sulfonic resin. In this article, the acidity of the KU-2-8-ZrO2 composites has been studied by the ammonia quasi-equilibrium thermo-desorption technique and their catalytic characteristics in etherification of isobutylene with ethanol were defined. The KU-2-8-ZrO2 productivity in this reaction was found to be an order of magnitude higher compared to KU-2-8 and several times higher compared to the commercial macroporous sulfonic resin Amberlyst 15. A high productivity of the KU-2-8-ZrO2 composites is achieved by the improved accessibility of the sulfonic resin acid sites for reagents. The composites do not swell in the polar medium and show high resistance to osmotic shock. The KU-2-8-ZrO2 composites with 70–80 wt % of KU-2-8 were found promising for industrial applications.

Anion structural effects on interaction of rare earth element ions with Dowex 50W X8 cation exchange resin

The effect of the anion in the original rare earth element (REE) solution on the reversible ion exchange of Ce nitrate and Ce sulfate with the Dowex 50W X8 was investigated using attenuated total reflection infrared (ATR-IR) spectroscopy, continuous flow reactor studies coupled with inductively coupled plasma mass spectroscopy (ICP-MS), and density functional theory (DFT). The simulated IR spectrum at the DFT B3LYP/6-31G(d) level was compared to the experimental results to characterize the IR spectrum, molecular interactions, and bonding of the ion exchanged species. The continuous liquid flow reactor studies show a capacity of 0.72 mmol/g sorbent for the Ce nitrateand 0.96 mmol/g sorbent for the Ce sulfate with the Dowex 50W X8. The flow reactor studies reveal the type of solute anion (SO4(2–) or NO3(−)) associated with the REE during cation exchange significantly affects the sorption capacity of the Dowex 50W X8 ion exchange resin. The calculated REE binding energy (BE) and the DFT optimized structures suggest that the differences in sorption capacity is the result of the formation of different types of partially ion-exchanged Ce2(3+)2SO4(2–) and Ce(3+) 3NO3(−). These results suggest that the solute anion affects the equilibrium constants of the Dowex resin by the formation of a charged layer capable of retaining the counterion. Modifying the sulfonic acid site (H+) in the Dowex 50W X8 with the NH4+ counterion does not affect the sorption capacity and retention times of the Ce nitrate and Ce sulfate species. These results suggest that the counterions and co-ions having a finite size, may limit access to the Dowex sulfonate active site where the type of REE cation as a nitrate or sulfate in solution may significantly modify the sorption capacity of the ion exchange resin. Similar results are obtained during sorption with nitrates and sulfates of Sm and Yb.

In-Situ Electrochemical Characterization of Proton Exchange Membranes for Water Electrolysis

Proton exchange membrane water electrolysis (PEM-WE) is a clean method for hydrogen production and an important piece in the adoption of a hydrogen fuel economy. Proton exchange membranes require specific chemical and physical properties for efficient use in the PEM-WE system, and development of these membranes still presents a major challenge. Current industry standards such as Nafion®, developed by DuPont, are costly, show high gas permeability, and are limited to operation below 90 °C.1 Performance of a novel sulfonated poly(arylene ether) membrane, SA8, is investigated in this research. SA8 has shown a significantly higher glass transition temperature than Nafion, better mechanical properties, higher proton conductivity, and better chemical stability from various ex-situ tests and in-situ fuel testing. The multiphenylated backbone creates free volume around the sulfonic acid sites, which allows for greater water uptake with minimal swelling.2 The presence of water is not only necessary for proton conductivity but is of particular importance in the water electrolyzer where the cell is fed liquid water, rather than operated at various humidities as in a fuel cell. In this research SA8 is found to successfully operate in a water electrolysis system at a temperature of 90 °C for over 120 hours. Polarization curves taken at 60 °C show operation of a 25 μm membrane at 1.8 V reaching a current density of 4 A cm-2. Ito, H., Maeda, T., Nakano, A. & Takenaka, H. International Journal of Hydrogen Energy (2011)Lee, H. F., Huang, Y.C., Wang, P.H., Lee, C.C., Hung, Y.S., Gopal, R., Holdcroft, S., Huang, W.Y. Mater. Today Commun. 3, 114–121 (2015).

A flexible metal–organic framework with a high density of sulfonic acid sites for proton conduction

The design of stable electrolyte materials with high proton conductivity for use in proton exchange membrane fuel cells remains a challenge. Most of the materials explored have good conductivity at high relative humidity (RH), but significantly decreased conductivity at reduced RH. Here we report a chemically stable and structurally flexible metal–organic framework (MOF), BUT-8(Cr)A, possessing a three-dimensional framework structure with one-dimensional channels, in which high-density sulfonic acid (–SO3H) sites arrange on channel surfaces for proton conduction. We propose that its flexible nature, together with its –SO3H sites, could allow BUT-8(Cr)A to self-adapt its framework under different humid environments to ensure smooth proton conduction pathways mediated by water molecules. Relative to other MOFs, BUT-8(Cr)A not only has a high proton conductivity of 1.27 × 10−1 S cm−1 at 100% RH and 80 °C but also maintains moderately high proton conductivity at a wide range of RH and temperature. Proton-conducting metal-organic frameworks (MOFs) could be used as the electrolytes in proton exchange membrane fuel cells but chemically stable materials that perform well at low humidity are still sought. Here the authors prepare a stable, structurally flexible MOF that maintains high proton conductivity under a wide range of humidity.

Oxygen Transport Effects of Cobalt Cation Contamination of Ionomer Thin Films in Proton Exchange Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are a promising automotive energy conversion technology for reducing the dependence on petroleum and reducing greenhouse gas emissions. However, the high cost of the platinum (Pt) electrocatalyst responsible for increasing the rate of the oxygen (O2) reduction reaction (ORR) in the cathode is one of the primary inhibitors to this technology’s mass market penetration. In order for PEMFCs to become cost competitive with internal combustion engine technologies, the electrocatalyst cost must be significantly reduced. To address this issue, the use of Pt alloys such as Pt3Co has been explored. Alloys such as Pt3Co have been shown to have higher activities than pure Pt electrocatalysts,(1) reducing the mass of the expensive Pt. However, the utilization of Pt3Co poses contamination risks to the ionomers used in PEMFCs due to cobalt’s (Co) propensity to dissolve out of the catalyst, migrate to the ionomer, and replace protons on the sulfonic acid sites(1). Cai et al.(2) demonstrated the effects of this risk through the testing of membrane electrode assemblies (MEAs) containing Co doped ionomers, which showed a decrease in proton conductivity through the ionomer. In addition, Kongkanand et al.(3) have shown that voltage losses at high current densities for low-Pt loaded electrodes can be attributed to localized O2 transport resistances in the thin films of ionomer covering the electrocatalyst surface. Thus, the effects of dissolved Co on the local O2 transport through these thin films of ionomer are of particular interest. The purpose of this work is to experimentally characterize the effects of Co contamination on the localized O2 transport properties of ionomer thin films. To study these effects, we modified an existing fuel cell to allow for the testing of gas (O2) transport through ionomer thin films in a well-controlled environment, similar to the setup used by Liu et al.(4) The setup allows for the films’ transport resistance to be measured under non-polarized (uniform Co distribution) and interface free conditions, in order to isolate the effect of the Co contamination. In addition, the setup allows for the control of the ionomer sample’s temperature and relative humidity, to evaluate the effects of each on the O2 transport resistance of the doped thin films. To test the effects of differing levels of Co cation contamination during PEMFC operation, we take O2 transport resistance measurements for various amounts of controlled Co ion doping. Our preliminary results have indicated significant increases in O2 transport resistances for high Co contamination levels, consistent with our hypotheses derived from the results mentioned above(2, 3). This work was partially supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy under grant DE-EE0007271. Figure 1

Ca2+ Effects on a Pt/C Catalyst for the Oxygen Reduction Reaction

The proton exchange membrane fuel cell (PEMFC) is one of the most promising renewable energy sources due to benign exhaust emissions and high energy efficiency. Pt/C is currently the primary catalyst for the slow oxygen reduction reaction (ORR) kinetics at the cathode of a PEMFC. The ORR, O2 + 4H+ + 4e- → 2H2O, indicates that this process preferentially occurs at a triple phase boundary where reactant, electrolyte, and catalyst are in contact [1, 2]. The depletion of O2, H+ or e- would significantly affect reaction kinetics. The Nafion® perfluorosulfonic acid (PFSA) ionomer, composed of a carbon-fluorine backbone and side chains ending with sulfonic acid groups, is conventionally used to prepare catalyst layers by exploiting its binding, proton-conducting and O2 transport properties. Foreign cations replace ionomer protons and occupy sulfonic acid sites by ion exchange [3-6]. The replacement of H+ by foreign cations in the ionomer decreases not only the proton conductivity but also O2 permeability. Uddin et al. [6] model results showed that the presence of Na+ in the ionomer of the cathode catalyst layer, which decreases the O2 permeability, causes a decrease in dissolved O2 concentration. Durst et al. [7] found that the diffusion coefficient and the concentration of O2 in the H2SO4 electrolyte, and the kinematic viscosity of the electrolyte decrease in the presence of Co2+. Cationic impurities decrease the membrane water content in turn shrinking the ionomer and lowering the active catalyst surface area. Also, foreign cations promote the generation of H2O2, a side product of the ORR, which exerts an undetermined influence on the performance and durability of PEMFCs. Literature and our group studies indicated that foreign cations have severe effects on the performance and durability of the PEMFC. Among all cations, Ca2+ deserves special attention because it is one of the most abundant elements within the earth’s crust. Prior efforts have focused on the effects of Ca2+ on PEMFC operation [8-10] and membrane transport properties [11]. However, the effects of Ca2+ on the ORR kinetics have hardly been studied. Okada et al. [12] studied the effects of Ca2+ on the O2 reduction kinetics at a Nafion® film covered Pt rotating disk electrode. Their results showed that impurity ions, even in small amounts, significantly hinder the rate of the O2 reduction charge transfer step. However, the Nafion® film covered Pt electrode is different from the supported catalyst layer for a PEMFC. The O2 transport properties in a Ca2+ form ionomer are poorly understood. In addition, the H2O2 yield has not been measured. In this presentation, detailed analyses of the changes in the Pt/C electrochemical surface area, ORR diffusion-limited and kinetic currents, Tafel slope, H2O2 yield, O2 permeability and ionomer sulfonate site occupation will be presented and discussed. Acknowledgments Authors are grateful to the United States Department of Energy (award DE-EE0000467), the Office of Naval Research (award N00014-12-1-0496), and the Hawaiian Electric Company.

Computational Modelling of Cationic Contamination in PEFCs: a Multiphase Mixture Approach

Cationic contamination in polymer electrolyte membrane fuel cells (PEFCs) can lead to accelerated degradation and loss of performance. There are several mechanisms to introduce these cationic impurities; including transport with the inlet fuel/air streams, or from degradation of the fuel cell and balance of plant components. Many common cations tend to have a higher affinity to the sulfonic acid side chains of the polymer electrolyte membrane (PEM) than protons, resulting in preferential uptake of these contaminants into the PEM. Once occupying these sites, the impurity cations contribute to the loss of performance by lowering the water content of the membrane and reducing the ionic conductivity.[1] To compliment experimental results, numerical studies have been performed[2,3] to understand the coupled impact of cation occupancy in the membrane with the water transport in the cell and the overall cell performance. Early generations of these models had assumed a constant cation occupancy in the cathode that was used as a boundary condition to solve the cation transport via a Stefan-Maxwell diffusion process. By coupling the contaminant occupancy to the water content of the membrane and electro-kinetics of the catalyst layers, cell performance has been shown to decrease down to as little as one third its non-contaminated levels.[3] This study builds off of previous models to develop a steady state, one dimensional, cation contamination model of a PEFC to examine the impact of cation transport to the membrane electrode assembly (MEA) via a water bridge across the gas diffusion layer (GDL) as shown in Figure 1. The multiphase mixture (M2) model, proposed by Wang and Cheng[4], is used to derive species transport equations for the reactant gases and water that permits two phase water transport in the GDL and catalyst layers. This resulting water distribution acts as to promote cation transport from the gas flow channels across the GDL, where the dissolved cations can evolve out of the liquid phase water and into the MEA, occupying the sulfonic acid sites of the membrane. A baseline non-contaminated case is presented to study the cell performance and species distribution normal operating conditions. Then, the model is employed to show how the saturation of the cathode effects cation distribution across the GDL and how the presence of dissolved cations in the catalyst layer impacts the contaminant occupancy and overall cell performance.

Infrared spectroscopy of ion-induced cross-linked sulfonated poly(ether ether ketone)

The dehydration of SPEEK-[H] (protonated sulfonated poly(ether ether ketone)) converts 3-fold symmetric (C3V) hydrated sulfonate sites to sulfonic acid sites with no local symmetry (C1). Like Nafion-[H], SPEEK-[H] C3V and C1 environments afford IR group modes (C3V,HF (1087 cm−1); C3V,LF (1026 cm−1) and C1,HF (1362 cm−1); C1,LF (904 cm−1)) due to the mechanical coupling of vibrational internal coordinates of an ether link with those of the sulfonate or sulfonic acid exchange site. C3V and C1 bands are inversely correlated during membrane hydration/dehydration. Hydrated SPEEK-[M] (M: Cu2+, Ni2+, Cd2+, Pb2+, Sr2+ or Ba2+) exhibits SPEEK-[H] C3V bands because cation waters of hydration preclude binding to the hydrated exchange site. When cation hydration spheres are thermally stripped at high vacuum, SPEEK-[M] C3V bands supplant SPEEK-[H] C3V bands, inducing SPEEK cross-linking. Incomplete cross-linking is evidenced by low intensities of SPEEK-[M] C1,HF bands. The 1362 cm−1 band intensities are inversely correlated with cation hydration enthalpies.

Biomass derived solid acids as effective hydrolysis catalysts

The conversion of cellulose into products with higher added value often includes a depolymerization step to obtain glucose, its fundamental unity. The depolymerization reaction is carried out via hydrolysis of the β-1,4-glycosidic bond. The search for a solid acid catalyst capable of breaking these bonds is gaining increasing prominence in the literature. In this regard, sulfonated carbons have shown promising results.This work evaluated the use of a residue from the extraction of palm oil as raw material for the production of sulfonated carbons. The raw material was carbonized and sulfonated. The obtained solid acids were tested in the hydrolysis of cellobiose, a dimer of glucose often used as a model compound for cellulose. The hydrolysis reaction is the first step in converting renewable carbon sources into chemical products and biofuels.Some aspects were investigated, as the effect of carbonization temperature on the concentration of sulfonic groups, the results showing that the content thereof reached a maximum value at 300°C. Regarding the hydrolysis of cellobiose, it has been identified that there is a relationship between the concentration of sulfonic acid groups and the activity of these catalysts. However, there is a drop in the turnover number as the amount of sulfonic acid sites increases. This was related to a preferred position sulfonation mechanism.Furthermore, sulfonated carbons showed higher activity than the commercial acid resins, indicating that this material may be a good option for the generation of solid acid catalysts.

Computational Modelling of Cation Contamination in PEFCs

Polymer electrolyte membrane (PEM) is a key component of polymer electrolyte membrane fuel cell (PEFC). It is vulnerable to cationic impurities that are present in the air and fuel stream or that may have originated from the cell, stack or balance of plant components. Almost all foreign cations have higher affinity to sulfonic acid group than proton and the presence of foreign cation in the membrane or catalyst layers results in reduced ionic conductivity, increased electro-osmotic drag, and reduced water content (1).In this study, a steady, one dimensional cation (Na+) contamination model of membrane electrode assembly (MEA) of PEFC (shown in figure 1) is developed by solving the coupled transport phenomena related to the foreign cation, water, and oxygen. Concentrated solution theory is utilized to solve the cation transport equation based on Serincan et al.’s model (2) and dilute solution theory for water, hydrogen, and oxygen transport. A spherical agglomerate model is considered in the cathode catalyst layer (CCL) to describe effects of foreign cations in the catalyst layer. To separate the effects of cations on different transport phenomena, first no contamination case is solved and then contamination effects are added one by one to the cation transport, water transport, and oxygen transport and finally to the Nernst equation.Cation (Na+) contamination in the air stream found to cause several detrimental effects on the performance of PEFC. The main effects are: (a) cation replaces proton and occupies sulfonic acid sites in ionomer. It can occupy up to 96% sites in the cathode catalyst layer (CCL); (b) It causes serious water depletion in the ionomer due to decrease in water diffusivity; (c) It decreases the oxygen diffusivity causing a decrease in dissolved oxygen concentration in CCL; and (d) It decreases the open circuit voltage (OCV) in CCL due to reduction in proton concentration in the ionomer phase. These contamination effects on each parameter decrease the protonic current density and combined effects result in a reduction of current density from 0.72 A/cm2 to 0.25 A/cm2at a cell voltage of 0.7 V (shown in figure 2). Acknowledgements The authors are grateful for the financial support of the Department of Energy (DOE)-EERE, DE-EE00000467 (University of Hawaii, prime contractor, Jean St-Pierre, PI).

Sulfonic acid heterogeneous catalysts for dehydration of C6-monosaccharides to 5-hydroxymethylfurfural in dimethyl sulfoxide

Sulfonic acid-functionalized heterogeneous catalysts have been evaluated in the catalytic dehydration of C 6 monosaccharides into 5-hydroxymethylfurfural (HMF) using dimethyl sulfoxide (DMSO) as solvent. Sulfonic commercial resin Amberlyst-70 was the most active catalyst, which was ascribed to its higher concentration of sulfonic acid sites as compared with the other catalysts, and it gave 93 mol% yield of HMF from fructose in 1 h. With glucose as the starting material, which is a much more difficult reaction, the reaction conditions (time, temperature, and catalyst loading) were optimized for Amberlyst-70 by a response surface methodology, which gave a maximum HMF yield of 33 mol% at 147 °C with 23 wt% catalyst loading based on glucose and 24 h reaction time. DMSO promotes the dehydration of glucose into anhydroglucose, which acts as a reservoir of the substrate to facilitate the production of HMF by reducing side reactions. Catalyst reuse without a regeneration treatment showed a gradual but not very significant decay in catalytic activity. Sulfonic acid-functionalized Amberlyst-70 was used in dimethyl sulfoxide (DMSO) as solvent for the catalytic dehydration of C 6 monosaccharides into 5-hydroxymethylfurfural (HMF), a biomass-derived platform molecule.

Computational Modeling of Foreign Cation Contamination in PEFCs

A steady-state, one dimensional computational model is developed to predict the effect of foreign cation contamination in polymer electrolyte fuel cells (PEFCs). The model solves the coupled transport phenomena of cations, oxygen, hydrogen, and water. Foreign cation (i.e. Na+) contamination in the air stream found to significantly decrease the performance of PEFC. The main effects are: (1) foreign cation replaces the proton and occupies the sulfonic acid sites in the ionomer. It can occupy up to 98% of the sites in the ionomer phase of the cathode catalyst layer (CCL). (2) It causes severe water depletion in the ionomer due to decrease in water diffusivity and equilibrium water uptake. (3) It decreases the oxygen diffusivity causing a decrease in dissolved oxygen concentration in CCL. (4) It also decreases the equilibrium potential due to reduction in proton concentration in the ionomer phase in cathode. These contamination effects on each parameter decrease protonic current density and combined effects result in a reduction of current density from 0.72 A/cm2 to 0.25 A/cm2 at a constant cell voltage of 0.7 V.

Copper modified exchanger for the photodegradation of methyl orange dye

AbstractA Cu modified hybrid exchanger was synthesized by loading Cu(II) onto the sulfonic acid sites of the C-145 cation exchanger by passing CuSO4 solution followed by treatment with sodium hydroxide to deposit the copper hydroxide particles. Each hybrid sorbent particle is essentially a spherical macroporous cation exchanger bead within which agglomerates of nanoscale hydrated Cu oxide particles have been uniformly and irreversibly dispersed using a simple chemical–thermal treatment. The obtained material was characterized using X-ray diffraction, energy-dispersive X-ray spectroscopy and scanning electron microscope. The obtained materials were applied for the photo-decolorization of methyl orange as a member of the azo dye family, in an aqueous medium using UV irradiation (λ = 254 nm) under different experimental conditions. The effect of catalyst concentration and pH on the decolorization of methyl orange dye was investigated. The decolorization of methyl orange dye has been followed using UV–vis spe...

Functionalized Carbon Nanofibers as Solid‐Acid Catalysts for Transesterification

Carbon nanofibers (CNFs) were functionalized with aryl sulfonic acid groups using in situ diazonium coupling. The use of diazonium coupling yielded an acidic carbon material, in which the introduced acidic groups are readily accessible to the triglyceride substrate. The material is an efficient catalyst for the transesterification of triolein and methanol, outperforming conventional sulfonated carbons in both stability and activity per acid site. Upon comparing CNFs with varying degrees of functionalization, a linear correlation between sulfonic acid sites and catalytic performance was found.

Efficient conversion of levulinic acid into alkyl levulinates catalyzed by sulfonic mesostructured silicas

Sulfonic mesoporous silicas have demonstrated an outstanding catalytic performance in the esterification of levulinic acid with different alcohols to produce alkyl levulinates, a family of chemicals considered to be excellent oxygenated fuel extenders for gasoline, diesel and biodiesel. Catalyst screening indicated that propylsulfonic acid-modified SBA-15 material was the most active one, among tested materials, due to a combination of moderately strong sulfonic acid sites with relative high surface hydrophobicity. Under optimized reaction conditions (T=117°C, ethanol/levulinic acid molar ratio=4.86/1 and catalyst/levulinic acid=7wt%) almost 100% of levulinic acid conversion was achieved after 2h of reaction, being negligible the presence of levulinic acid by-products or ethers coming from intermolecular dehydration of alcohols. The catalyst has been reused, without any regeneration treatment, up to three times keeping almost the high initial activity. Interestingly, a close catalytic performance to that achieved using ethanol has been obtained with bulkier alcohols.