Low Hydrogen Partial Pressure Research Articles

In vitro reduction of methane production by 3-nitro-1-propionic acid is dose-dependent1.

Methanogenesis is a metabolic process that allows the rumen ecosystem the ability to maintain the low hydrogen partial pressures needed for proper digestive function. However, rumen methanogenesis is considered to be an inefficient process because it can result in the loss of 4% to 12% of the total energy consumed by the host. Recent studies have shown that some short-chain nitrocompounds such as nitroethane, 2-nitroethanol, 2-nitro-1-propanol, and 3-nitro-1-propionic acid (3NPA) are capable of inhibiting the production of methane during in vitro culture; nevertheless, optimal supplementation doses have yet to be determined. In the present study, in vitro cultures of freshly collected mixed populations of ruminal microbes were supplemented with the naturally occurring nitrocompound, 3NPA, to achieve 0, 3, 6, 9, or 12 mM. Analysis of fermentation products after 24 h of incubation revealed that methane (CH4) production was reduced in a dose-dependent manner by 29% to 96% (P < 0.05) compared with the amount produced by untreated controls (15.03 ± 0.88 µmol mL-1 incubated liquid). Main effects of the supplement were also observed, which resulted in a reduction (P < 0.05) on amounts of total gas and volatile fatty acids (VFA) produced, as well as in an increase of 0.07 to 0.30 µmol mL-1 on rates of 3NPA degradation. Changes in production of metabolites as CH4, hydrogen (H2), VFA, and NH3 indicated that the fermentation efficiency was not compromised dramatically by 3NPA treatment in moderate doses of 6 and 9 mM. Results further revealed that the metabolism of the 3NPA by microbial populations is also dose-dependent. The microbes were able to metabolize more than 75% of the added nitrocompound, with the greatest degradation rates in cultures treated with 9-mM 3NPA. Finally, from a practical standpoint, and considering the magnitude of CH4 reduction, effect on VFA, and percentage of metabolized supplement, the most efficacious dose for 3NPA administration may be between 3 and 9 mM.

All-Iron Hybrid Flow Batteries with In-Tank Rebalancing

Principles of sealed iron flow batteries are introduced and a semi-empirical model that incorporates the hydrogen evolution reaction and electrolyte rebalancing is developed. Hydrogen generation rates are measured using pressure measurements in sealed vessels. Electrolyte dynamics with and without electrolyte rebalancing are simulated and discussed, and a good agreement is found between measured and simulated pressure responses. The sealed battery system with in-tank rebalancing demonstrates stable operation at low hydrogen partial pressure during 10 days and 100 cycles at ± 100 mA cm−2 at room temperature.

Y2O3-Inserted Co-Pd/zeolite catalysts for reductive amination of polypropylene glycol

Cobalt-based catalysts having different base strengths were prepared by controlling the amount of yttrium oxide (Y2O3). These catalysts were used for the facile one-pot synthesis of polyetheramine (PEA) from polypropylene glycol (PPG) through reductive amination. It is noticed that high hydrogen partial pressures up to 40 bar inhibit the formation of cobalt nitride and lead to a high PEA yield although it has been known that dehydrogenation from alcohol to ketone is the rate-determining step. The Y2O3-inserted Co-Pd/Molecular sieve13X catalyst also showed high activity toward PEA even at low hydrogen partial pressure. Y2O3 played a crucial role in giving basicity to the catalyst, which not only prevents the formation of cobalt nitride but also promotes hydrogenation of imine to amine at a wide range of H2 pressure. Thus Y2O3 inserted Co-Pd/Molecular sieve 13X provides unique performance toward enhancing the PEA yield while suppressing the catalyst deactivation caused by the cobalt nitride formation.

Advanced impedance study of polymer electrolyte membrane single cells by means of distribution of relaxation times

Electrochemical impedance spectroscopy data of a polymer electrolyte membrane fuel cell are compiled across a wide range of operating conditions. In all cases, homogeneous operating conditions are applied over the entire cell area to set a clearly defined operating point and to derive unambiguous parameter dependencies. As a novelty, this diverse set of impedance spectra is deconvoluted by the distribution of relaxation times (DRT) method in the frequency range from 0.5 Hz to 60 kHz. In H2/air-operation five polarization contributions with different time constants are registered. The assignment to gas diffusion in the gas diffusion layer and catalyst layer, the oxygen reduction reaction at the Pt-catalyst and proton transport processes in the cathode catalyst layer is supported by a systematic analysis of parameter dependencies.Furthermore, DRT deconvolution in H2/H2-operation reveals three “new” anode contributions, usually hidden by the dominating cathode contributions. They are assigned to gas diffusion and hydrogen oxidation, including charge-transfer and proton transport in the anode catalyst layer. It is confirmed that the polarization contributions at the cathode side sum up to 96% for typical operating conditions, but the share changes to 80% cathode and 20% anode at low hydrogen partial pressure.

Theoretical evaluation of Pd[sbnd]Ag membrane reactor performance during biomass steam gasification for hydrogen production using CFD method

In recent years, biomass has been introduced as a promising solution for environmental crisis. Biomass steam gasification is a valuable process for hydrogen production. Main problem of this process is low conversion and low partial pressure of hydrogen in product stream. PdAg membrane reactor (MR) can be used in biomass steam gasification to improve the process efficiency. Hence, Computational fluid dynamic (CFD) method was used in this study for a detail modeling and analyzing the biomass steam gasification in a two-dimensional PdAg MR. After good agreement of CFD model results with literature experimental data, simulation results was indicated that the PdAg MR has better efficiency compared with traditional reactor (TR). Biomass conversion of near 100%, CO selectivity in the range 0–14 and H2 recovery of 70% in the best condition were achieved. In addition, different flow patterns (cocurrent and counter-current modules) were compared for MR and overall efficiency (biomass conversion) of counter-current model was obtained higher than co-current model. In summary, for all operating conditions and modules, PdAg MR was showed better efficiency compared with TR.

Methane steam reforming using a membrane reactor equipped with a Pd-based composite membrane for effective hydrogen production

Herein, a methane steam reforming (MSR) reaction was carried out using a Pd composite membrane reactor packed with a commercial Ru/Al2O3 catalyst under mild operating conditions, to produce hydrogen with CO2 capture. The Pd composite membrane was fabricated on a tubular stainless steel support by the electroless plating (ELP) method. The membrane exhibited a hydrogen permeance of 2.26 × 10−3 mol m2 s−1 Pa−0.5, H2/N2 selectivity of 145 at 773 K, and pressure difference of 20.3 kPa. The MSR reaction, which was carried out at steam to carbon ratio (S/C) = 3.0, gas hourly space velocity (GHSV) = 1700 h−1, and 773 K, showed that methane conversion increased with the pressure difference and reached 79.5% at ΔP = 506 kPa. This value was ∼1.9 time higher than the equilibrium value at 773 K and 101 kPa. Comparing with the previous studies which introduced sweeping gas for low hydrogen partial pressure in the permeate stream, very high pressure difference (2500–2900 kPa) for increase of hydrogen recovery and very low GHSV (<150) for increase hydraulic retention time (HRT), our result was worthy of notice. The gas composition monitored during the long-term stability test showed that the permeate side was composed of 97.8 vol% H2, and the retentate side contained 67.8 vol% CO2 with 22.2 vol% CH4. When energy was recovered by CH4 combustion in the retentate streams, pre-combustion carbon capture was accomplished using the Pd-based composite membrane reactor.

Syntrophomonas wolfei Uses an NADH-Dependent, Ferredoxin-Independent [FeFe]-Hydrogenase To Reoxidize NADH.

ABSTRACTSyntrophomonas wolfei syntrophically oxidizes short-chain fatty acids (four to eight carbons in length) when grown in coculture with a hydrogen- and/or formate-using methanogen. The oxidation of 3-hydroxybutyryl-coenzyme A (CoA), formed during butyrate metabolism, results in the production of NADH. The enzyme systems involved in NADH reoxidation in S. wolfei are not well understood. The genome of S. wolfei contains a multimeric [FeFe]-hydrogenase that may be a mechanism for NADH reoxidation. The S. wolfei genes for the multimeric [FeFe]-hydrogenase (hyd1ABC; SWOL_RS05165, SWOL_RS05170, SWOL_RS05175) and [FeFe]-hydrogenase maturation proteins (SWOL_RS05180, SWOL_RS05190, SWOL_RS01625) were coexpressed in Escherichia coli, and the recombinant Hyd1ABC was purified and characterized. The purified recombinant Hyd1ABC was a heterotrimer with an αβγ configuration and a molecular mass of 115 kDa. Hyd1ABC contained 29.2 ± 1.49 mol of Fe and 0.7 mol of flavin mononucleotide (FMN) per mole enzyme. The purified, recombinant Hyd1ABC reduced NAD+ and oxidized NADH without the presence of ferredoxin. The HydB subunit of the S. wolfei multimeric [FeFe]-hydrogenase lacks two iron-sulfur centers that are present in known confurcating NADH- and ferredoxin-dependent [FeFe]-hydrogenases. Hyd1ABC is a NADH-dependent hydrogenase that produces hydrogen from NADH without the need of reduced ferredoxin, which differs from confurcating [FeFe]-hydrogenases. Hyd1ABC provides a mechanism by which S. wolfei can reoxidize NADH produced during syntrophic butyrate oxidation when low hydrogen partial pressures are maintained by a hydrogen-consuming microorganism.IMPORTANCE Our work provides mechanistic understanding of the obligate metabolic coupling that occurs between hydrogen-producing fatty and aromatic acid-degrading microorganisms and their hydrogen-consuming partners in the process called syntrophy (feeding together). The multimeric [FeFe]-hydrogenase used NADH without the involvement of reduced ferredoxin. The multimeric [FeFe]-hydrogenase would produce hydrogen from NADH only when hydrogen concentrations were low. Hydrogen production from NADH by Syntrophomonas wolfei would likely cease before any detectable amount of cell growth occurred. Thus, continual hydrogen production requires the presence of a hydrogen-consuming partner to keep hydrogen concentrations low and explains, in part, the obligate requirement that S. wolfei has for a hydrogen-consuming partner organism during growth on butyrate. We have successfully expressed genes encoding a multimeric [FeFe]-hydrogenase in E. coli, demonstrating that such an approach can be advantageous to characterize complex redox proteins from difficult-to-culture microorganisms.

Syntrophic acetate oxidation during the two-phase anaerobic digestion of waste activated sludge: Microbial population, Gibbs free energy and kinetic modelling

A system using a two-phase anaerobic configuration (mesophilic/thermophilic) was tested by feeding waste activated sludge (WAS). The first acidogenic stage presented a hydraulic retention time (HRT) of 3 days, while the second methanogenic stage had an HRT of 10 days. Both raw and ultrasonically pretreated WAS samples were utilized for the experiment. Previous Fluorescence in Situ Hybridization (FISH) observations, revealed that in the thermophilic phase, the acetoclastic methanogenesis was likely replaced by a nonacetoclastic pathway, namely, syntrophic acetate oxidation (SAO). A modified version of Anaerobic Digestion Model n°1 (ADM1), accounting for the SAO pathway, was implemented and calibrated. The proposed model addressed the relationship between the hydrogen concentration and Gibbs free energy and showed the thermodynamic feasibility of the SAO pathway, while simultaneously highlighting the role played by hydrogenotrophic methanogens in maintaining a sufficiently low hydrogen partial pressure so that the SAO was energetically feasible. The estimated energy loss was estimated to be approximately 20% due to the switch of the microbial pathway from acetoclastic methanogenesis to SAO.

Microbial electrosynthesis of butyrate from carbon dioxide: Production and extraction

To date acetate is the main product of microbial electrosynthesis (MES) from carbon dioxide (CO2). In this work a tubular bioelectrochemical system was used to carry out MES and enhance butyrate production over the other organic products. Batch tests were performed at a fixed cathode potential of −0.8V vs SHE. The reproducibility of the results according to previous experiments was validated in a preliminary test. According to the literature butyrate production could take place by chain elongation reactions at low pH and high hydrogen partial pressure (pH2). During the experiment, CO2 supply was limited to build up pH2 and trigger the production of compounds with a higher degree of reduction. In test 1 butyrate became the predominant end-product, with a concentration of 59.7mMC versus 20.3mMC of acetate, but limitation on CO2 supply resulted in low product titers. CO2 limitation was relaxed in test 2 to increase the bioelectrochemical activity but increase pH2 and promote the production of butyrate, what resulted in the production of 87.5mMC of butyrate and 34.7mMC of acetate. The consumption of ethanol, and the presence of other products in the biocathode (i.e. caproate) suggested that butyrate production took place through chain elongation reactions, likely driven by Megasphaera sueciensis (>39% relative abundance). Extraction and concentration of butyrate was performed by liquid membrane extraction. A concentration phase with 252.4mMC of butyrate was obtained, increasing also butyrate/acetate ratio to 16.4. The results are promising for further research on expanding the product portfolio of MES.

Optimizing renewable oil hydrocracking conditions for aviation bio-kerosene production

In the present work we have performed a parameter study to maximize the yields of aviation bio-kerosene and renewable diesel range products obtained from the conversion of plant-oil triglycerides over Ni–W/SiO2–Al2O3, hydrocracking catalyst. Specific insights and changes in reaction mechanisms, with CO bond breaking favoured at increased pressures (>60bar) leading to depropanation/deoxygenation, as compared to CC bond breaking becoming favoured at reduced pressures (<60bar) leading to formation of lower range esters and short chain glycerides, are established for the first time using analytical techniques (GC, NMR and IR). The CC cleavage and low hydrogen partial pressures (<60bar) led to formation of unsaturated intermediates, which promoted cyclization, aromatization and coking reactions, which increased deactivation of catalyst. High space time yield with a maximum of 240ml/(h⋅Lcatalyst) for <C9 products and 350ml/(h⋅Lcatalyst) for C9–C14 products was observed at 420°C temperatures. Stable catalytic performance was observed until 450h of continuous operation with 25–30% yield of aviation bio-kerosene which meets all ASTM D 7566 standards.

Microbial ecology overview during anaerobic codigestion of dairy wastewater and cattle manure and use in agriculture of obtained bio-fertilisers

The anaerobic co-digestion of dairy wastewater (DW) and cattle manure (CM) was examined and associated with microbial community’s structures using Denaturing Gradient Gel Electrophoresis (DGGE). The highest volatile solids (VS) reduction yield of 88.6% and biogas production of 0.87L/g VS removed were obtained for the C/N ratio of 24.7 at hydraulic retention time (HRT) of 20days. The bacterial DGGE profile showed significant abundance of Uncultured Bacteroidetes, Firmicutes and Synergistetes bacterium. The Syntrophomonas strains were discovered in dependent association to H2-using bacteria such as Methanospirillum sp., Methanosphaera sp. and Methanobacterium formicicum. These syntrophic associations are essential in anaerobic digesters allow them to keep low hydrogen partial pressure. However, high concentrations of VFA produced from dairy wastes acidification allow the growth of Methanosarcina species. The application of the stabilised anaerobic effluent on the agriculture soil showed significant beneficial effects on the forage corn and tomato plants growth and crops.

CMOS Compatible Growth of High Quality Ge, SiGe and SiGeSn for Photonic Device Applications

Epitaxial growth of group IV materials on Si has been widely explored for integration of active and passive opto-electronic devices in integrated circuits. In order to meet the limitations imposed by complementary-metal-oxide-semiconductor (CMOS) technology, low temperature growth (below 450 ºC) has been pursued through different methods [1]. Achieving high quality growth at low temperatures is a challenge due to low decomposition rate of SiH4 and GeH4 and lower surface mobilty of adatoms. Propagation of threading dislocations and poor crystallinity of the films deteriorates optical efficiency and electronic transport properties of the film. Reduction of threading dislocation density of the Ge films have been achieved by different methods such as graded SiGe buffer layers, low-temperature:high-temperature (LT:HT) growth of Ge layer and annealing at elevated temperatures [2-4]. In this paper, we report on the role of different carrier gases (Ar, N2 and H2) in LT:HT growth of Ge layers by chemical vapor deposition (CVD) to attain low threading dislocation density (TDD) films. The optimized growth conditions have been applied for the growth of SiGe and SiGeSn films using SnD4 as Sn precursor. Propagation of defects in Ge rich films are mainly due to the threading of the screw dislocation throughout the film. Growth of a sacrificial layer like SiGe or LT Ge, results in reduction of threading dislocation through graded lattice change or merging of the defects [5]. The transport and reactions of the precursors are highly affected by the carrier gas in CVD processes. The carrier gases play a significant role in transferring the energy to the precursor molecules in the gas phase as well as affecting the deposition on the surface [6]. Larger gas molecules have higher cross-section with the precursors to transfer the energy and break the bonds before reaching the surface. On the other hand, presence of hydrogen in the precursor gases cause, the surface of the sample to be covered with hydrogen after the ad-species are bonded with the surface. Hydrogen as carrier gas increases the partial pressure of hydrogen which lowers the adsorption of ad-species to and desorption of byproducts from the surface. Ar or N2 gases lower the partial pressure of hydrogen and change the balance in favor of ad-species adsorption and hydrogen desorption during deposition. This results in a lesser competition between ad-species adsorption and hydrogen desorption. Fig.1 a shows the X-ray diffraction (XRD) patterns of the Ge films deposited using different carrier gases. The growth was performed using a HT:LT mechanism at 300-550 ºC temperature. The results show that Ge growth in Ar ambient has higher quality in comparison with N2 and H2 which is attributed to the larger size of Ar and lower hydrogen partial pressure at the surface. The cross-sectional transmission electron microscopy (TEM) image of growth with Ar ambient shows TDD as low as 1.3×107 cm-2 [Fig.1(b)]. Growth in N2 and H2 show poor quality as seen in the XRD patterns [Fig.1(a)]. SiGe and SiGeSn films were grown using the optimized conditions for Ge growth. A complete study of growth from 0.1 torr to 1 torr, at temperatures from 350-450 ºC for different precursor flow rates is performed. Silicon incorporation in Ge films varied from 1% to 28% for SiGe films [Fig.1(a)]. Tin incorporation of 2% was observed in the films with 13% to 17% Si incorporation [Fig.1(a)]. Investigation of film quality has been done using etch pit measurement with Schimmel solution for 10 minutes. The comparison of TDD using TEM (1.3×107 cm-2) and SEM images (1.7×107 cm-2) for Ge films confirm the accuracy of the measurements. Figs.1 (c), (d), and (e) show the scanning electron microscopy image (SEM) of etch pit Ge, SiGe and SiGeSn films respectively. The TDD of SiGe growth is 2.3 ×107 cm-2 , while the TDD of SiGeSn film is 4.0 ×107 cm-2. Our investigations show that high quality growth of Ge, SiGe and SiGeSn films has been achieved using Ar carrier gas at CMOS compatible temperatures. The material characterization of Ge films show optimized growth condition using Ar carrier gas. Low TDD of SiGe and SiGeSn films show high quality material growth that can be used for optoelectronic device applications.

Unraveling the mechanism of propanoic acid hydrodeoxygenation on palladium using deuterium kinetic isotope effects

A combined experimental and computational kinetic isotope effect (KIE) study was performed for the catalytic hydrodeoxygenation (HDO) of deuterium-labeled propanoic acid (PAc-2, 2-D2) over Pd catalyst. For the experimental study, the kinetics were measured in a plug flow reactor over a 5wt% Pd/C catalyst at 200°C and 1atm under differential conversion using a reactor feed consisting of 1.2% PAc and 5% or 20% H2, with balance helium. Different experimental KIE values for the high (kH/kD=1.13±0.04) and low (kH/kD=1.62±0.05) partial pressures of hydrogen were observed. Density functional theory calculations were performed to obtain the reaction parameters of the elementary steps involved in the HDO of PAc on Pd (111), and a microkinetic model was developed to estimate the KIE for the low hydrogen partial pressure case from first principles. The computed result (kH/kD=1.49) is in good agreement with the experiment. In addition, the product distribution favored C2H6 and CO, suggesting decarbonylation (DCN) is the main reaction pathway. This provides strong evidence for the proposed mechanism for the formation of C2H6 on both Pd (111) and supported Pd nanoparticles presenting primarily that exposed crystal face.

Power generation characteristics of a SOFC with a Ni/YSZ anode incorporating a SrZr&lt;sub&gt;0.95&lt;/sub&gt;Y&lt;sub&gt;0.05&lt;/sub&gt;O&lt;sub&gt;3-α&lt;/sub&gt; proton conductor

In order to improve the performance and stability of anodes for solid oxide fuel cells (SOFCs) under low hydrogen concentration conditions, SrZr0.95Y0.05O3-α (SZY) proton conductor particles were incorporated into the conventional Ni/YSZ anode. Power generation experiments were conducted using the electrolyte-supported single cells with conventional Ni/YSZ and Ni/YSZ-5%SZY anodes. Enhanced output power density under low hydrogen partial pressure conditions was achieved with the modified anode. This enhancement is ascribed to a decline in the anode overpotential of the Ni/YSZ-5%SZY anode, estimated from impedance spectra, compared to that of the conventional Ni/YSZ anode. In addition, the amount of hydrogen adsorption on Ni, YSZ, and SZY was measured using thermal desorption spectroscopy (TDS). This revealed that the proton conductor SZY could adsorb a large amount of hydrogen compared with YSZ. Consequently, the SZY proton conductor may play an important role in the supply/storage of adsorbed hydrogen, or in increasing the oxidation resistance of Ni under low hydrogen concentration conditions.

Preparation and Performance of Catalytic Hollow Fibre Membranes for Hydrogenation Reduction of Nitrites in Water

Porous Al2O3 hollow fiber membranes have been fabricated via a phase inversion – sintering technique. Pd-loaded carbon nanotubes (CNTs) are formed inside the hollow fibre wall by the catalytic decomposition of methane over Fe particles, followed by impregnation and reduction with hydrogen to form catalytic hollow fibre membranes. Hydrophobic modification of the hollow fibres is conducted by gas permeable polymeric coating. The resultant hollow fibre membranes exhibit highly catalytic activity to the hydrogenation reduction of nitrites in aqueous solution. Hollow fibre membrane reactors are assembled for nitrite hydrogenation by pumping nitrite solution into the tube side and introducing hydrogen countercurrently to the shell side of the reactor. The nitrite removal in the hollow fibre membrane reactors increases with the operation temperature and the hydrogen feed concentration at lower hydrogen partial pressures, but less influenced by the hydrogen feed concentration when it is higher than 50%. A higher nitrite concentration favors the nitrite hydrogenation reaction but lowers the nitrite removal efficiency.

Comparative study of the performance of an anaerobic rotating biological contactor and its potential to enrich hydrogenotrophic methanogens

BACKGROUND Process upset due to volatile fatty acid accumulation is one of the major drawbacks of anaerobic treatment of wastewater. The performance of an anaerobic rotating biological contactor (AnRBC) was studied under normal operating conditions as well as shock loadings of propionic acid, for its ability to enhance the conversion of hydrogen to methane. These results were compared with those of a reactor lacking the enhanced gas-liquid hydrogen transfer mechanism, a conventional anaerobic digester. RESULT The AnRBC exhibited lower concentrations of hydrogen in the headspace (300–600 ppm) under both normal and shock loading conditions, and also showed more hydrogenotrophic methanogens on the denaturing gradient gel electrophoresis (DGGE) profile of 16S rRNA gene amplicons, both in terms of intensity and band numbers (4 in the AnRBC and 2 in the anaerobic digester). CONCLUSION This study showed that the AnRBC is able to maintain lower hydrogen partial pressure at both normal operating and shock loading conditions due to the abundance of hydrogenotrophic methanogens and good gas–liquid hydrogen transfer efficiency. This finding should encourage the commercial exploitation of AnRBC for the treatment of wastewaters, especially that containing easily acidifiable organic compounds, which causes instability in operation through souring. © 2014 Society of Chemical Industry

C223 プロトン伝導体SZY添加燃料極がSOFC出力特性に及ぼす効果(OS6 水素・燃料電池(2))

For solid oxide fuel celt, a new anode with proton conductor made of Strontium Zirconium Yttrium oxide (SZY, SrZr_<0.95>Y_<0.05>O_<3-a>) was investigated. Power generation experiments were conducted using a single cell with Ni/YSZ incorporating 5%SZY anode. It was disclosed that the output density of the cell with Ni/YSZ-5%SZY anode was higher than that with Ni/YSZ anode under the condition of low partial pressure of hydrogen. In addition, alternative impedance measurement was conducted and from impedance spectra, anode overpotential was estimated. By adding 5%SZY to Ni/YSZ, the anode overpotential was decreased under the condition of low hydrogen partial pressure. At the situation of a low concentration hydrogen supply, it is expected that the SZY proton conductor might play an important role in hydrogen supply and/or storage similar to the case of BCY proton conductor.

Composite cathode based on doped vanadate enhanced with loaded metal nanoparticles for steam electrolysis

The use of composite electrodes based on La0.7Sr0.3VO3 (LSV) for steam electrolysis has uncovered the tremendous potential and capacity inherent in this material. Unfortunately, this material has a major setback of inefficient electrolysis triggered by limited electrocatalytic activity. In this work, an infiltration method is employed to load catalytic-active metal nanoparticles onto the composite electrodes in order to achieve an activity-enhanced electrode performance. The electrical properties of LSV are methodically explored and correlated to electrode performance. At 800 °C in either pure H2 or low hydrogen partial pressure (pH2) of 5%H2/N2, the polarization resistance of symmetrical cells with Ni-loaded LSV (LSV-Ni) cathode is largely enhanced, in contrast to bare LSV cathode. Similar improvement is also achieved for the Fe-loaded LSV (LSV-Fe) cathode in a wide range of hydrogen partial pressures of 5%–100%. The Faraday efficiencies of LSV-Ni and LSV-Fe composite cathodes were remarkably improved for electrolysis in either 3%H2O/4.7H2/Ar or 3%H2O/Ar at 800 °C.

Production of biohydrogen from sugars and lignocellulosic biomass using Thermoanaerobacter GHL15

The effect of culture parameters on hydrogen production using strain GHL15 in batch culture was investigated. The strain belongs to the genus Thermoanaerobacter with 98.9% similarity to Thermoanaerobacter yonseiensis and 98.5% to Thermoanaerobacter keratinophilus with a temperature optimum of 65–70 °C and a pH optimum of 6–7. The strain metabolizes various pentoses, hexoses, and disaccharides to acetate, ethanol, hydrogen, and carbon dioxide. However substrate inhibition was observed above 10 mM glucose concentration. Maximum hydrogen yields on glucose were 3.1 mol H2 mol−1 glucose at very low partial pressure of hydrogen. Hydrogen production from various lignocellulosic biomass hydrolysates was investigated in batch culture. Various pretreatment methods were examined including acid, base, and enzymatic (Celluclast® and Novozyme 188) hydrolysis. Maximum hydrogen production (5.8–6.0 mmol H2 g−1 dw) was observed from Whatman paper (cellulose) hydrolysates although less hydrogen was produced by hydrolysates from other examined lignocellulosic materials (maximally 4.83 mmol H2 g−1 dw of grass hydrolysate). The hydrogen yields from all lignocellulosic hydrolysates were improved by acid and alkaline pretreatments, with maximum yields on grass, 7.6 mmol H2 g−1 dw.

Influence of Reaction Parameters on the First Principles Reaction Rate Modeling of a Platinum and Vanadium Catalyzed Nitro Reduction

This paper describes the influence of key reaction parameters on the development of a rate model which can be used to forecast starting material conversion independent of scale. A nitro reduction was examined via first principles reaction progress modeling. The reaction parameters, most notably hydrogen partial pressure and agitation rate, influenced the choice of rate model. At lower hydrogen partial pressures, the reaction rate was influenced by gas to liquid mass transfer, hydrogen pore diffusion, and the rate of the surface reaction during the course of the overall reaction. No single model could be generated to explain the rate observations at lower hydrogen partial pressures. At higher hydrogen partial pressures, a kinetic reaction model was used to generate an equation to forecast the substrate concentration as a function of time and reaction parameters. This reaction model was confirmed to be independent of scale provided that the mass transfer coefficient exceeded a minimum threshold value. The m...