Effect of fly ash and H2S on a Ni-based catalyst for the upgrading of a biomass-generated gas

The main concern about the technology for the production of hydrogen and transport fuels by biomass gasification is the presence of contaminants (H₂S, tars, fly ash, alkali, and heavy metals, ammonia) that are poisonous for the catalysts used for upgrading the biomass-generated gas. The impact of the main contaminants on a Ni/MgAl(O) reforming catalyst was studied in a laboratory environment, by exposing the studied sample to H₂S, NH₃, K₂SO₄, KCl, ZnCl₂, and a solution derived from biomass fly ash. Lastly, the catalyst was also streamed with a gas produced by a bench-scale downdraft gasifier. The extent of deactivation was examined in the methane steam reforming reaction, under different operational conditions. The main effect of the treatments was a decrease in the bulk surface area and in the metal dispersion. Streaming H₂S quickly deactivated the catalyst; however, the activity was recovered by increasing the inlet temperature or by adding O₂ to the stream. In further laboratory tests, the performances of the catalyst seemed not to be greatly affected by either the above treatments or by the presence of ammonia in the fed water. The catalyst produced a syngas composition close to that predicted at equilibrium even after being streamed with the biomass-generated gas.     

A proton-conducting solid state H2S-O2 fuel cell. 1. anode catalysts, and operation at atmospheric pressure and 20–90°C

A stable solid state H₂S--O₂ fuel cell has been developed and operated at 1 atm and 20-90°C. A series of anode catalysts has been examined using Nafion^® as a common proton conducting membrane; those containing Pd and Pt were found to be effective using H₂ or H₂S as the anode feed gas, but MoS₂--C catalysts were effective for use of H₂S but not for H₂. The highest potential attained using H₂S and Pd/C catalyst was 722 mV (theory: 1140 mV). When H₂S was used as anode feed the potential decreased up to 35% over 24 h as sulfur was deposited on the anode. The efficiency of the cell increased with temperature up to 90°C.     

Reduction of hydrogen peroxide production at anode of proton exchange membrane fuel cell under open-circuit conditions using ruthenium–carbon catalyst

This study examines the effect of hydrogen peroxide (H₂O₂) on the open-circuit voltage (OCV) of a proton exchange membrane fuel cell (PEMFC) and the reduction of H₂O₂ in the membrane using a ruthenium/carbon catalyst (Ru/C) at the anode. Each cathode and anode potential of the PEMFC in the presence of H₂O₂ is examined by constructing a half-cell using 1.0 M H₂SO₄ solution as an electrolyte and Ag/AgCl as the reference electrode. H₂O₂ is added to the H₂SO₄ solution and the half-cell potential is measured at each H₂O₂ concentration. The cathode potential is affected by the H₂O₂ concentration while the anode potential remains stable. A Ru catalyst is used to reduce the level of H₂O₂ formation through O₂ cross-over at the interface of a membrane and the anode. The Ru catalyst is known to produce less H₂O₂ through oxygen reduction at the anode of PEMFC than a Pt catalyst. A Ru/C layer is placed between the Nafion^® 112 membrane and anode catalyst layer and the cell voltage under open-circuit condition is measured. A single cell is constructed to compare the OCV of the Pt/C only anode with that of the Ru/C-layered anode. The level of hydrogen cross-over and the OCV are determined after operation at a current density of 1 A cm⁻² for 10 h and stabilization at open-circuit for 1 h to obtain an equilibrium state in the cell. Although there is an increase in the OCV of the cell with the Ru/C layer at the anode, excessive addition of Ru/C has an adverse effect on cell performance.     

Synthesis and characterization of osmium carbonyl cluster compounds with molecular oxygen electroreduction capacity

A transition metal cluster electrocatalyst based on Os_x(CO)_n was synthesized by pyrolysis of Os₃(CO)₁₂ in 1,2-Dichlorobenzene (b.p.≈180°C) under inert atmosphere (N₂). The electrocatalytic parameters of the oxygen reduction reaction (ORR) for an Os_x(CO)_n catalyst were studied with a rotating disk electrode in 0.5 MH₂SO₄ electrolyte. The diffusion coefficient and solubility of O₂ in 0.5 MH₂SO₄ were calculated. Koutecky–Levich analysis of the linear voltamperometry data showed that the reaction follows first-order kinetics and the value of the Koutecky–Levich slope indicates a multielectron charge transfer during the ORR. The value of the Tafel slope obtained from the mass transfer corrected Tafel plots is 131 mV/decade. The performance of the catalyst in a H₂/O₂ PEM fuel cell cathode was evaluated and found to be nearly as good as that of Pt.     

Two-step steam pretreatment of softwood by dilute H2SO4 impregnation for ethanol production

Fuel ethanol can be produced from softwood through hydrolysis in an enzymatic process. Prior to enzymatic hydrolysis of the softwood, pretreatment is necessary. In this study two-step steam pretreatment by dilute H₂SO₄ impregnation to improve the overall sugar and ethanol yield has been investigated. The first pretreatment step was performed under conditions of low severity (180°C, 10 min, 0.5% H₂SO₄) to optimise the amount of hydrolysed hemicellulose. In the second step the washed solid material from the first pretreatment step was impregnated again with H₂SO₄ and pretreated under conditions of higher severity to hydrolyse a portion of the cellulose, and to make the cellulose more accessible to enzymatic attack. A wide range of conditions was used to determine the most favourable combination. The temperatures investigated were between 180°C and 220°C, the residence times were 2, 5 and 10 min and the concentrations of H₂SO₄ were 1% and 2%.

The effects of pretreatment were assessed by both enzymatic hydrolysis of the solids and with simultaneous saccharification and fermentation (SSF) of the whole slurry, after the second pretreatment step. For each set of pretreatment conditions the liquid fraction was fermented to determine any inhibiting effects. The ethanol yield using the SSF configuration reached 65% of the theoretical value while the sugar yield using the SHF configuration reached 77%. Maximum yields were obtained when the second pretreatment step was performed at 200°C for 2 min with 2% H₂SO₄. This form of two-step steam pretreatment is a promising method of increasing the overall yield in the wood-to-ethanol process.     

NOx and H2S formation in the reductive zone of air-staged combustion of pulverized blended coals

Low NO_x combustion of blended coals is widely used in coal-fired boilers in China to control NO_x emission; thus, it is necessary to understand the formation mechanism of NO_x and H₂S during the combustion of blended coals. This paper focused on the investigation of reductive gases in the formation of NO_x and H₂S in the reductive zone of blended coals during combustion. Experiments with Zhundong (ZD) and Commercial (GE) coal and their blends with different mixing ratios were conducted in a drop tube furnace at 1200°C–1400°C with an excessive air ratio of 0.6–1.2. The coal conversion and formation characteristics of CO, H₂S, and NO_x in the fuel-rich zone were carefully studied under different experimental conditions for different blend ratios. Blending ZD into GE was found to increase not only the coal conversion but also the concentrations of CO and H₂S as NO reduction accelerated. Both the CO and H₂S concentrations inblended coal combustion increase with an increase in the combustion temperature and a decrease in the excessive air ratio. Based on accumulated experimental data, one interesting finding was that NO and H₂S from blended coal combustion were almost directly dependent on the CO concentration, and the CO concentration of the blended coal combustion depended on the single char gasification conversion.Thus, CO, NO_x, and H₂S formation characteristics from blended coal combustion can be well predicted by single char gasification kinetics.     

Electrochromic properties of lithiated Co-oxide (LixCoO2) and Ni-oxide (LixNiO2) thin films prepared by the sol–gel route

Layered Li_xCoO₂ and Li_xNiO₂ thin films (x1) were prepared by a peroxo wet chemistry route from Li(I), Co(II) and Ni(II) acetate precursors and the addition of H₂O₂. Structural changes during the processing of xerogel to final oxide were followed by X-ray diffraction and infrared spectroscopy. Electrochromic properties were determined with in-situ potentiodynamic, potentiostatic and galvanostatic spectroelectrochemical measurements. Single dipped films with composition Li_0.99Co_1.01O₂ or Li_0.94Ni_1.06O₂ exhibited stable voltammetric response in 1 M LiClO₄/propylene carbonate electrolyte after about 60 cycles. The total charge exchanged in a reversible charging/discharging cycle was about ±30 mC cm⁻² for Li_0.99Co_1.01O₂ and ±20 mC cm⁻² for Li_0.94Ni_1.06O₂ oxide films. Galvanostatic measurements showed that about 1/2 (x0.5) and 2/3 (x0.3) of Li⁺ ions could be reversibly removed from the structure of Li_0.99Co_1.01O₂ and Li_0.94Ni_1.06O₂ films, respectively. Practical applicability of Li_0.99Co_1.01O₂ and Li_0.94Ni_1.06O₂ oxide films was studied in electrochromic devices with WO₃(H⁺)Li⁺ormolyteLi_0.99Co_1.01O₂ and WO₃(H⁺)Li⁺ormolyteLi_0.94Ni_1.06O₂ configuration. The monochromatic transmittance T_s (λ=633 nm) of dark blue coloured devices was extremely low (T_s3%), whereas in bleached state the value reached around T_s70%.     

Applicability of molten carbonate fuel cells to various fuels

MCFCs can utilize CO rich and H₂ lean fuel, such as gasified biomass or gasified waste as a Pt catalyst is not used and Pt poisoning by CO does not occur. This feature has become very important due to the worldwide CO₂ depression requirements. CRIEPI has developed MCFC technologies in line with a governmental program, which mainly focused on natural gas fuel. However, CRIEPI has recently been focussing on technologies for various fuel applications. Single cells and stacks were tested with various gas compositions and showed stable performance even with high CO and high fuel utilization conditions. Gasified biomass or waste can contain many kinds of impurities such as H₂S, HCl, HF, NH₃, etc. The effects of these impurities were taken into account for single cells, and the permissible limits were estimated.     

Photoelectrocatalytic generation of H2 and S from toxic H2S by using a novel BiOI/WO3 nanoflake array photoanode

In this paper, a photoelectrocatalytic (PEC) recovery of toxic H₂S into H₂ and S system was proposed using a novel bismuth oxyiodide (BiOI)/ tungsten trioxide (WO₃) nano-flake arrays (NFA) photoanode. The BiOI/WO₃ NFA with a vertically aligned nanostructure were uniformly prepared on the conductive substrate via transformation of tungstate following an impregnating hydroxylation of BiI₃. Compared to pure WO₃ NFA, the BiOI/WO₃ NFA promotes a significant increase of photocurrent by 200%. Owing to the excellent stability and photoactivity of the BiOI/WO₃ NFA photoanode and I^–/{\mathrm{I}}_{\mathrm{3}}^{-} catalytic system, the PEC system toward splitting of H₂S totally converted S^2– into S without any polysulfide ({\mathrm{S}}_x^{n-}) under solar-light irradiation. Moreover, H₂ was simultaneously generated at a rate of about 0.867 mL/(h·cm). The proposed PEC H₂S splitting system provides an efficient and sustainable route to recover H₂ and S.     

Ag/Al2O3(Li2O)/g-C3N4光催化乙醇制取环氧乙烷

本文制备了一系列Ag/Al₂O₃(Li₂O)/g-C₃N₄复合催化剂,考察了其可见光催化乙醇制取环氧乙烷的性能。Li₂O可调变Al₂O₃表面的酸性,从而降低了主要副产物乙醛的选择性。Ag/Al₂O₃(Li₂O) 在g-C₃N₄上的负载量对产物环氧乙烷的选择性有较大影响,当Ag/Al₂O₃(Li₂O) 负载量为5wt%时,乙醇具有较高的转换率,且环氧乙烷的选择性高达100%。     

Reduction of NiAl2O4 containing catalysts for steam methane reforming reaction

Reducibility of a NiAl₂O₄ containing catalyst was studied. On a measurement of NiAl₂O₄ concentration in a catalyst, a peak area ratio of NiAl₂O₄ in XRD analysis was verified to express the NiAl₂O₄ concentration. The reducibility of NiAl₂O₄ was confirmed to be dependent on the calcining temperature to form NiAl₂O₄, not dependent on the calcining time. The catalyst containing NiAl₂O₄ was ascertained to be reduced under convenient conditions to actual plant operations; H₂/N₂ = 30/70 at 1023K for 1 h + steam/CH₄ = 6 at 1023K for 17 h.     

Lithium insertion into manganese dioxide electrode in MnO2/Zn aqueous battery: Part I. A preliminary study

The discharge characteristics of manganese dioxide (γ-MnO₂ of electrolytic manganese dioxide (EMD) type) as a cathode material in a Zn–MnO₂ battery containing saturated aqueous LiOH electrolyte have been investigated. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) data on the discharged material indicate that lithium is intercalated into the host structure of EMD without the destruction of its core structure. The XPS data show that a layer of insoluble material, possibly Li₂CO₃, is deposited on the cathode, creating a barrier to H₂O, thus preventing the formation of Mn hydroxides, but allowing the migration of Li ions into the MnO₂ structure. The cell could be reversibly charged with 83% of voltaic efficiency at 0.5 mA/cm² current density to a 1.9 V cutoff voltage. The percentage utilization of the cathode material during discharge was 56%.     

Studies on cerium (Ce/Ce)–vanadium(V/V) redox flow cell—cyclic voltammogram response of Ce/Ce redox couple in H2SO4 solution

A novel Ce⁴⁺/Ce³⁺–V²⁺/V³⁺ redox flow cell has been designed. The electrochemical responses of higher concentration Ce⁴⁺/Ce³⁺ couple in H₂SO₄ solution were investigated via cyclic voltammetry. The normal potential and the kinetic parameters for anodic oxidation of Ce³⁺ and cathodic reduction of Ce⁴⁺ were measured. The results showed the surface of platinum electrode was fully covered with type I oxide that inhibited the reduction of Ce⁴⁺. The reversibility of the Ce⁴⁺/Ce³⁺ couple improved with the increase of H₂SO₄ concentration. Different electrochemically active substances existed at various state of charge (SOC) and the reversibility of the Ce⁴⁺/Ce³⁺ couple at the carbon electrode was superior to platinum.     

Activity and corrosion of tungsten carbide recombination electrodes during lead/acid battery operation

The oxidation of the tungsten carbide (WC) catalyst in recombination electrodes partially immersed in H₂SO₄ solution was investigated when the electrodes operated in an atmosphere of oxygen and hydrogen. It has been established that after a long operation period (400 h) 60 to 70% of the catalysts, depending on the initial active surface of WC, may be oxidized to WO_x, whereby the rate of recombination decreases about three times. It is assumed that the oxidation of WC is due to the H₂O₂ formed as an intermediate product of the recombination of hydrogen and oxygen. Silver accelerates the decomposition of H₂O₂ and hence the use of a WC—Ag mixture as catalyst in the recombination electrodes reduces strongly the carbide corrosion.     

Enhancing the photoelectrochemical performance of p-silicon through TiO2 coating decorated with mesoporous MoS2

MoS₂ is a promising electrocatalyst for hydrogen evolution reaction and a good candidate for cocatalyst to enhance the photoelectrochemical (PEC) performance of Si-based photoelectrode in aqueous electrolytes. The main challenge lies in the optimization of the microstructure of MoS₂, to improve its catalytic activity and to construct a mechanically and chemically stable cocatalyst/Si photocathode. In this paper, a highly-ordered mesoporous MoS₂ was synthesized and decorated onto a TiO₂ protected p-silicon substrate. An additional TiO₂ necking was introduced to strengthen the bonding between the MoS₂ particles and the TiO₂ layer. This meso-MoS₂/TiO₂/p-Si hybrid photocathode exhibited significantly enhanced PEC performance, where an onset potential of +0.06 V (versus RHE) and a current density of −1.8 mA/cm² at 0 V (versus RHE) with a Faradaic efficiency close to 100% was achieved in 0.5 mol/L H₂SO₄. Additionally, this meso-MoS₂/TiO₂/p-Si photocathode showed an excellent PEC ability and durability in alkaline media. This paper provides a promising strategy to enhance and protect the photocathode through high-performance surface cocatalysts.     

Selective removal of CO from hydrogen-rich stream over CuO/CexSn1−xO2–Al2O3 catalysts

The solid solutions of Ce_xSn_1−xO₂ incorporated with alumina to form Ce_xSn_1−xO₂–Al₂O₃ mixed oxides, by the suspension/co-precipitation method, were used to prepare CuO/Ce_xSn_1−xO₂–Al₂O₃ catalysts for the selective oxidation of CO in excess hydrogen. Incorporating Al₂O₃ increased the dispersion of Ce_xSn_1−xO₂, but did not change their main structures and did not weaken their redox properties. Doping Sn⁴⁺ into CeO₂ increased the mobility of lattice oxygen and enhanced the activity of the 7%CuO/Ce_xSn_1−xO₂–Al₂O₃ catalyst in the selective oxidation of CO. The selective oxidation of CO was weakened as the doped fraction of Sn⁴⁺ exceeded 0.5. Incorporating appropriate amounts of Sn⁴⁺ and Al₂O₃ could obtain good candidates 7%CuO/Ce_xSn_1−xO₂–Al₂O₃(20%), 1–x=0.1–0.5, for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5%Pt/Al₂O₃.     

Biodiesel production from mahua (Madhuca indica) oil having high free fatty acids

A technique to produce biodiesel from mahua oil (Madhuca indica) having high free fatty acids (19% FFA) has been developed. The high FFA level of mahua oil was reduced to less than 1% by a two-step pretreatment process. Each step was carried out with 0.30–0.35 v/v methanol-to-oil ratio in the presence of 1% v/v H₂SO₄ as an acid catalyst in 1-hour reaction at 60°C. After the reaction, the mixture was allowed to settle for an hour and methanol–water mixture that separated at the top was removed. The second step product at the bottom was transesterified using 0.25 v/v methanol and 0.7% w/v KOH as alkaline catalyst to produce biodiesel. The fuel properties of mahua biodiesel were found to be comparable to those of diesel and conforming to both the American and European standards.     

Impedance measurements of air-oxidized and H2-annealed Raney-Ni catalysts for alkaline fuel cells

The catalytic properties and the long-term performance of Raney-NiTi2 catalysts being used in H₂ electrodes of alkaline H₂---O₂ fuel cells can be significantly improved by slow air oxidation and subsequent annealing in an H₂ atmosphere at 300°C. Individual reaction steps are investigated by means of impedance measurements. Theoretical estimations, on the basis of a simple equivalent circuit of a supported electrode, result in a frequency-response relationship which is in very good agreement with the experimental data referring to the relevant frequency range of 10⁻³−10⁻¹ Hz. A method to evaluate the impedance spectra is described in some detail. Calculated and measured impedance data are in good agreement, thus indicating the validity of the charge transfer resistance, the diffusion resistance, as well as the chemisorption capacity and the double-layer capacity. Experiments on the influence of catalyst annealing in an H₂ atmosphere at 350°C show a strong increase in the charge transfer resistance and an obvious decrease in the diffusion resistance, depending on the annealing time. A similar influence on the chemisorption capacity and the double-layer capacity is not observed.     

A rechargeable lithium battery employing a porous thin film of Cu3+δMo6S7.9

Porous, thin films of copper molybdenum sulfides (Cu_3+δMo₆S_7.9), that have been prepared by the technique of painting and subsequent reaction with mixed H₂/H₂S gases at 500 °C, have been used as a cathode material for lithium secondary batteries. The test cell comprised: Li/2 M LiClO₄ in PC-THF (4:6)/Cu_3+δMo₆S_7.9 (porous, thin film). The discharge reaction proceeded via the intercalation of lithium ions into the structural interstices of the cathode material.

The first discharge curve of the cell showed that the porous film could incorporate up to 18 lithium ions per formula unit. The capacity of the thin film was four times higher than that previously reported for powder or pressed-pellet electrodes. The theoretical energy density was 675 W h kg⁻¹, i.e., higher than that of TiS₂ (455 W h kg⁻¹) which is one of the best materials for high-energy lithium batteries. From X-ray diffraction studies of the lithium incorporated in the thin film at each discharge step, it is suggested that there are four incorporation reactions of lithium ions into the cathode. Finally, cycling tests have been conducted at room temperature.     

Probing the reaction pathway of dehydrogenation of the LiNH2 + LiH mixture using in situ H NMR spectroscopy

Using variable temperature in situ ¹H NMR spectroscopy on a mixture of LiNH₂ + LiH that was mechanically activated using high-energy ball milling, the dehydrogenation of the LiNH₂ + LiH to Li₂NH + H₂ was investigated. The analysis indicates NH₃ release at a temperature as low as 30 °C and rapid reaction between NH₃ and LiH at 150 °C. The transition from NH₃ release to H₂ appearance accompanied by disappearance of NH₃ confirms unambiguously the two-step elementary reaction pathway proposed by other workers.