H2 N2 Research Articles

Enhanced non-enzymatic glucose sensing of Cu–BTC-derived porous copper@carbon agglomerate

Porous copper@carbon agglomerate (PCCA) is prepared by pyrolysis of Cu3(BTC)2·3H2O (Cu–BTC, BTC = 1,3,5-benzenetricarboxylic acid) in 5% H2–N2 mixture atmosphere. The phase and morphology evolution are thoroughly examined by XRD, Raman, BET, TG, XPS, SEM and TEM, respectively. The results show that PCCA is formed at 400 °C and maintains the cubic morphology of the original Cu–BTC crystal. PCCA is composed by round-shaped copper nanoparticles that covered outside by thin layer of carbon. The non-enzymatic glucose sensing properties of PCCA-modified glassy carbon electrode (Cu/GCE) are characterized by cyclic voltammetry. The sensor shows high sensitivity of 614.3 µA mM−1 to glucose oxidation and negligible responses toward interference from uric acid, ascorbic acid, dopamine and l-cysteine at the level of their physiological concentrations. The sensor also exhibits rapid response (< 6 s), wide linear range (up to 3.33 mM) and low detection limit (0.29 µM at signal/noise ratio (S/N) = 3). Finally, the good stability, reproducibility and repeatability to glucose detection make PCCA a promising catalyst for non-enzymatic glucose sensor.

Monitoring of hydrogen concentration using capacitive nanosensor in a 1% H 2 –N 2 mixture

In this work, a hydrogen capacitor nanosensor with palladium nanoparticles (PdNPs) electrode based on metal–oxide–semiconductor structure has been fabricated. The capacitor sensor has been fabricated on the n-type silicon substrate with an oxide film thickness of 50 nm. PdNPs are synthesised and then deposited on the oxide surface using spin coating. PdNPs are characterised using by transmission electron microscope and UV spectrum. Also, the morphology of the oxide surface is characterised using by atomic force microscope. The response time and recovery time of nanosensor have been explained at the room temperature. The time interval to 90% of the signal value for 1% H2–N2 mixture was 1.4 s and recovery time was 14 s. The curve of pressure as a function of hydrogen concentration (H/Pd) in the PdNPs and the mechanism of the nanosensor are reported. The capacitor nanosensor based on nanoparticles shows sensitive and fast response.

Hydrodeoxygenation of Methyl Laurate over Ni Catalysts Supported on Hierarchical HZSM-5 Zeolite

The hierarchical HZSM-5 zeolite was prepared successfully by a simple NaOH treatment method. The concentration of NaOH solution was carefully tuned to optimal the zeolite acidity and pore structure. Under NaOH treatment conditions, a large number of mesopores, which interconnected with the retained micropores, were created to facilitate mass transfer performance. There are very good correlations between the decline of the relative zeolite crystallinity and the loss of micropores volume. The Ni nanoclusters were uniformly confined in the mesopores of hierarchical HZSM-5 by the excessive impregnation method. The direct deoxygenation in N2 and hydrodeoxygenation in H2 of the methyl laurate were compared respectively over the Ni/HZSM-5 catalysts. In the N2 atmosphere, the deoxygenation rate of the methyl laurate on the Ni/HZSM-5 catalyst is relatively slow. In the presence of H2, the synergistic effect between the hydrogenation function of the metal and the acid function of the zeolite supports can make the deoxygenation level more obvious. The yield of hydrocarbon products gradually reached the maximum with the appropriate treatment concentration of 1M NaOH, which could be attributed to the improved mass transfer in the hierarchical HZSM-5 supports.

Pulsed Acoustic Hydrogen Analyzers

A construction diagram for pulsed acoustic gas analyzers is considered. Mathematical modeling showed that pulsed acoustic gas analyzers for hydrogen in binary gas mixtures H2–He, H2–CH4, H2–NH3, H2–CO, H2–N2, H2–C2H2, and H2–CO2 can in fact be built. The main metrological characteristics (static conversion function, sensitivity, relative measurement error) of these devices are analyzed.

Comparison of Fast Response and Recovery Pd Nanoparticles and Ni Thin Film Hydrogen Gas Sensors Based on Metal-Oxide-Semiconductor Structure

In this study, two hydrogen sensors with Pd/SiO2/Si and Ni/SiO2/Si structures have been fabricated. Palladium nanoparticles are synthesized and then deposited on the oxide surface using spin coating. Capacitance–voltage curves for the Pd/SiO2/Si sensor at room temperature and for the Ni/SiO2/Si sensor at 140[Formula: see text]C in pure nitrogen and 1% H2–N2 mixture are described. The time required for reaching 90% of the steady-state signal magnitude ([Formula: see text]) for Pd/SiO2/Si capacitor was 1.4[Formula: see text]s and for Ni/SiO2/Si capacitor was 90 s. The time interval for recovery from 90% to 10% of steady-state signal magnitude ([Formula: see text] for Pd/SiO2/Si capacitor was 14[Formula: see text]s and for Ni/SiO2/Si capacitor was 40[Formula: see text]min. For the Pd/SiO2/Si capacitor, the response is 88% and for Ni/SiO2/Si capacitor the response is 29%. Comparison of Pd nanoparticles capacitive- and resistance-based sensors shows that the metal-oxide-semiconductor capacitive is faster and more sensitive than the resistance-based hydrogen gas sensors.

Low-temperature stability of body-centered cubic PdCu membranes

Concerns about limited durability at ambient temperatures are a major obstacle for the utilization of Pd-type membranes for H2 purification in local, on-demand H2 production. It is clear that pure Pd membranes are not suitable for applications that involve fast regular start-up and shut-down of purification systems but knowledge remains sparse about the performance of Pd alloy membranes in such situations. Here we investigated the stability of thin-layered, supported PdCu membranes with body-centered cubic (bcc) structure between room temperature and 673K at H2 pressure differences ΔPH2 up to 1MPa. Three PdCu layers with 46–50% Pd have been prepared by alternating electrodeposition of multiple Cu and Pd layers onto metallized ceramic membranes and subsequent alloying at 673–773K. The H2 permeation rates of all membranes can be described by single permeation laws in the entire investigated temperature range. The nominal H2 permeability of a Pd48Cu52 membrane amounted to 2.3 × 10−9molm−1s−1Pa−0.5 at 673K and ΔPH2 = 100kPa with an ideal H2/N2 selectivity of 3382. The H2 fluxes and N2 leak rates of the three membranes were not affected by cycling between room temperature and 673K under up to 1.1MPa H2 which included more than a dozen H2/N2 exchanges at 298K. These fluxes remained also stable through 100h continuous operation in H2 at that temperature. The excellent low-temperature tolerance of these membranes is attributed to the marginal hydrogen solubility in bcc PdCu alloys rendering them promising membrane materials for H2 purification involving everyday operation at ambient temperatures.

Mechanism of Iron Oxide Scale Reduction in 5%H2–N2 Gas at 650–900 °C

The reduction behaviour of the oxide scale on hot-rolled, low-carbon steel strip in 5%H2–N2 gas at 650–900 °C was studied. In general, the reduction rate of the oxide scale at the centre location was more rapid than that at the near-edge location. In both cases, the reduction rates at 650 °C were extremely low and the rates increased with increased temperature, reaching their maxima at 850 °C. Arrhenius plot of the rate constant derived from the early parabolic stage revealed that the reduction mechanism at 650–750 °C differed from that at 750–850 °C, with the former being oxygen diffusion in α-Fe and the latter most likely iron diffusion in wustite. In all cases, a thin iron layer formed on the scale surface within a very short time and then the thickness of this layer remained essentially unchanged, while the scale layer was gradually reduced via outward migration of the inner wustite–steel interface, as a result of inward iron diffusion through the wustite layer to that interface. More rapid oxygen diffusion through the thin surface iron layer than the oxygen supply rate through interface reaction was believed to result in a lower oxygen potential at the outer iron–wustite interface, thus providing a driving force for iron to diffuse through the wustite layer. The inner wustite–iron interface became undulating initially; then with the rapid advance of some protruding sections, some parts of the wustite layer were reduced through first, and finally the remaining wustite islands were reduced to complete the reduction process. Porosities were generated when wustite islands were reduced due to localized volume shrinkage. Higher oxygen concentrations in the scales of the near-edge samples were believed to be responsible for their slower reduction rates than those of the centre location samples.

Synthesis of titanium oxycarbonitride by carbothermal reduction and nitridation of ilmenite with recycling of polyethylene terephthalate (PET)

An innovative and sustainable carbothermal reduction and nitridation (CTRN) process of ilmenite (FeTiO3) using a mixture of polyethylene terephthalate (PET) and coal as the primary reductant under an H2–N2 atmosphere was proposed. The use of PET as an alternative source of carbon not only enhances the porosity of the pellets but also results in the separation of Fe from titanium oxycarbonitride (TiO x C y N z ) particles because of the differences in surface tension. The experiments were carried out at 1250°C for 3 h using four different PET contents ranging from 25wt% to 100wt% in the reductant. X-ray diffraction (XRD), scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDX), and LECO elemental analysis were used to study the phases and microstructures of the reduced samples. In the case of 75wt% PET, iron distinctly separated from the synthesized TiO x C y N z phase. With increasing PET content in the sample, the reduction and nitridation rates substantially increased. The synthesis of an oxycarbonitride with stoichiometry of TiO0.02C0.13N0.85 with minimal intermediate titanium sub-oxides was achieved. The results also showed that the iron particles formed from CTRN of FeTiO3 exhibited a spherical morphology, which is conducive for Fe removal via the Becher process.

Plasma enhanced atomic layer deposition of molybdenum carbide and nitride with bis(tert-butylimido)bis(dimethylamido) molybdenum

Molybdenum carbonitride films were deposited using plasma enhanced atomic layer deposition techniques with (tBuN)2(NMe2)2Mo at temperatures ranging from 80 to 300 °C. The elemental composition of the molybdenum carbonitride films were analyzed using x-ray photoelectron spectroscopy with a MoCxNy composition extending from carbide, MoC0.45N0.08 to nitride MoC0.06N1.40 (x: 0.06–0.45; y: 0.08–1.40). The film composition, electrical properties, and optical properties are strongly dependent upon the % N2 in H2 of the plasma gas stream, as well as the process temperature. The molybdenum carbide film (MoC0.45N0.08) deposited at 150 °C achieved an electrical resistivity (ρ) value of 170 μΩ cm and exhibited superconducting behavior with a transition temperature (Tc) of 8.8 K. Nitrogen rich molybdenum carbonitride films (MoC0.28N0.44) deposited at 250 °C with 6% N2 in the plasma gas showed a microcrystalline fine grained structure with a measured ρ = 200 μΩ cm. Film thickness and optical properties were characterized using spectroscopic ellipsometry with a measured growth per cycle extending from 0.36 to 0.56 Å/cycle. The measured optical properties extend across a broad range; refractive index (n: 3.1–3.4), and dielectric constant (k: 1.5–3.18). Grazing incidence x-ray diffraction of the MoCxNy films indicate a fine grained crystal structure, with a transition from a cubic MoC1−x phase for the carbide to a face center cubic γ-Mo2N1±x phase for the nitride films.

Plasma-assisted atomic layer deposition of HfNx: Tailoring the film properties by the plasma gas composition

The authors synthesized HfNx (x ≥ 1) thin films by plasma-assisted atomic layer deposition at stage temperatures of 350–450 °C by using the high-thermal-stability CpHf(NMe2)3 monomer as Hf precursor and either H2 plasma or N2 plasma as coreactant. Most notably, the selection of the plasma gas composition enabled us to tune the film properties: films fabricated using N2 plasma led to the formation of highly resistive and amorphous Hf3N4 films (6 × 102 Ω cm), while the use of the strongly reducing H2 plasma generated conductive (resistivity of 6 × 10−1 Ω cm) films with the signature of the δ-HfN fcc crystal structure. Via x-ray photoelectron spectroscopy, the authors observed that the use of the H2 plasma facilitates the reduction of the oxidation state of Hf from Hf4+ to Hf3+. This result was corroborated by the simultaneous increase in the free carrier absorption observed in the infrared range via spectroscopic ellipsometry. The δ-HfNx films fabricated via the present route are promising as highly reflective back contacts for thin films solar cells, Cu diffusion barriers, and as a gate metal for metal–oxide–semiconductor capacitors, provided that the resistivity values can be further decreased by suppressing the formation of the resistive Hf2ON2 impurity phase and grain-boundary scattering of the charge carriers.

Chemistry and kinetics of the pyrophoric plutonium hydride-air reaction

The chemistry and kinetics of the pyrophoric reaction of the plutonium hydride solid solution (PuHx, 1.9 ≤ x ≤ 3) are derived from pressure-time and gas analysis data obtained after exposure of PuH2.7 to air in a closed system. The reaction is described by two sequential steps that result in reaction of all O2, partial reaction of N2, and formation of H2. Hydrogen formed by indiscriminate reaction of N2 and O2 at their 3.71:1 M ratio in air during the initial step is accommodated as PuH3 inside a product layer of Pu2O3 and PuN. H2 is formed by reaction of O2 and partial reaction of N2 with PuH3 during the second step. Both steps of reaction are described by general equations for all values of x. The rate of the first step is proportional to the square of the O2 pressure, but independent of temperature, x, and N2 pressure. The second step is a factor of ten slower than step one with its rate controlled by diffusion of O2 through a boundary layer of product H2 and unreacted N2. Rates and enthalpies of reaction are presented and anticipated effects of reactant configuration on the heat flux are discussed.

The effects of hydrogen dilution, carbon monoxide poisoning for a Pt–Ru anode in a proton exchange membrane fuel cell

The effects of carbon monoxide (CO) poisoning and hydrogen dilution are investigated for a series of simulated reformate gases. A simple mathematical model with an internal air bleed term is proposed to understand the interaction between CO poisoning, hydrogen dilution, and the internal air bleed (IAB). According to the steady-state modeling results, the presence of nitrogen can be considered as a diluting agent for a relatively dilute H2–N2 mixture. For a CO–H2–N2 mixture, hydrogen dilution and CO poisoning “magnify” each other in their combined effect on the surface coverage of hydrogen. The beneficial effect of IAB was found to be affected by the competitive adsorption between CO and hydrogen. The steady-state surface coverage of CO is influenced by the adsorption and desorption of CO, the interaction between CO and the electro-oxidation of hydrogen, the interaction between IAB/hydrogen dilution/CO, the interaction between IAB/CO. However, the steady-state surface coverage of CO is largely determined by its own adsorption and desorption properties. Analytical solutions are also derived from the proposed mode for the transient surface coverage of hydrogen and CO. The mathematical treatment has been proved extremely effective for the understanding of the steady-state and transient behavior of the CO–H2 and CO–H2–N2 mixtures.

Preferential oxidation of carbon monoxide on Pt/γ-Al2O3 catalyst: Effect of adding ceria and nickel

The effect of adding ceria and nickel to Pt/γ-Al2O3 catalyst was studied for preferential oxidation (PROX) of CO. The catalysts were characterized by XRD, BET, TPR, XRF and H2 chemisorption techniques. An optimum amount of ceria and nickel was required for improving the activity and selectivity. Adding small amount of ceria (1 wt. %) and/or nickel (1 wt. %) improved the activity and selectivity of 1% Pt/γ-Al2O3 catalyst. When 1 wt. % of both the promoters i.e. ceria and nickel were added to 1% Pt/γ-Al2O3 catalyst, a significant improvement was observed in its activity and selectivity. With 1%Pt-1%Ni/1%CeO2/γ-Al2O3 catalyst, complete CO conversion was obtained even at 100 °C for a feed containing 1% CO, 1% O2, 40% H2 and balance N2. This novel catalyst also widened the temperature range of operation for complete CO conversion from 100 to 200 °C and no methanation activity was observed in this temperature range. The high activity and selectivity of this catalyst was most likely due to the formation of bimetallic Pt–Ni phase on the catalyst and higher dispersion of Pt metal on the catalyst as observed from H2 chemisorption.

Ammonia Synthesis at Intermediate Temperatures from N2 and Steam in Solid-State Electrochemical Cells Using Cesium Hydrogen Phosphate Based Electrolytes

Solid-state electrochemical synthesis of ammonia is promising to overcome the limited conversion of the conventional catalytic reactors [1] and to enable ammonia synthesis in more mild conditions. Several electrochemical reactors based on the following electrolytes: polymers, perovskites, fluorites, pyrochlores, and composite electrolytes, were investigated to synthesize ammonia from N2 and H2. The highest NH3 formation rate reported so far for an electrochemical system was found to be 1.13×10-8 mol cm-2 s-1 using a Nafion membrane, wet H2 and dry N2 at 80 °C and atmospheric pressure [2]. For N2-H2O ammonia synthesis Amer et al. reported 4.0×10-10 mol cm-2 s-1 at375ºC [3]. In this research ammonia synthesis was performed using solid-state electrochemical cells, for the first time, at an intermediate temperature of 220 °C and atmospheric pressure. Composites composed of CsH2PO4 and SiP2O7 were used as the electrolyte and various noble metals as the anode and cathode catalysts. The effects of the applied voltage and electrode catalysts on the NH3 formation rate and Faradaic efficiency were investigated.CsH2PO4 was prepared by dissolving stoichiometric quantities of Cs2CO3 and H3PO4 in distilled water and drying overnight at 120 °C. SiP2O7 was prepared from mesoporous SiO2 and H3PO4 as reported previously [4]. As electrode catalysts Pt/C-loaded carbon paper (Pt loading 1 mg cm-2, ElectroChem Inc.), Ru-loaded carbon paper, and Ag/Pd paste (TR-4865, Tanaka Kikinzoku Kogyo K.K.) were used. The Ru-loaded carbon paper was prepared by liquid phase reduction of RuCl3 by NaBH4, followed by filtration of the metallic Ru particles using a carbon paper. The membrane electrode assembly (MEA) was prepared by uniaxial pressing. The molar ratio of CsH2PO4 and SiP2O7 in the mixture was 2:1. The anode, electrolyte, and cathode were placed in a die, layer by layer, and then uniaxially pressed at pressure of 250 MPa for 10 min. When the Ag/Pd paste was used as the electrode catalyst, a thin layer (~0.1 mm in thickness) of the catalyst paste was pasted onto the surface of the electrolyte pellet. In ammonia synthesis, humidified N2 was supplied to the cathode chamber, and humidified H2 or humidified Ar to the anode chamber. The feed gas flow rates were 50 cm3 min-1. A water concentration of 30 % was obtained by bubbling the gas flow through water at 70 °C.Figure 1 summarizes ammonia synthesis rate from N2 and H2 for different applied voltages. The largest ammonia synthesis rate was 2.4×10-10 mol cm-2 s-1 at 0.3 V when the Pt/C was used as the cathode. Over the Ru and Ag-Pd cathodes the ammonia synthesis rate decreased monotonically for the increase in the applied voltages. A similar trend in the Faradaic efficiency, which designates the ratio of the current used for ammonia synthesis, was observed for the increase in the applied voltage. This means that H2 is preferentially formed at the cathode for the high applied voltages. The current density increased at the high applied voltages and it is probable that the coverage of the cathode surface by protons becomes high, leading to suppression of N2 adsorption to the cathode surface and preferential formation of H2. This is partially evidenced by the low NH3 formation rate over the Ag/Pd cathode which is less active for dissociation of N2.N2-H2O ammonia synthesis was carried out by feeding water vapor to the anode. The ammonia synthesis rate at 1.2 V was decreased to the order of 10-11 mol cm-2 s-1, compared with the N2-H2 synthesis. The anode might be inefficient for water electrolysis. The ammonia synthesis rate normalized to electrochemically active surface area of each cathode was compared. It was found that the Ru cathode is most active for ammonia synthesis. This result indicates that the catalyst active for dissociation of N-N bond is also requisite in electrochemical ammonia synthesis when the adsorption sites at the cathode surface are available for N2 adsorption.[1] I.A. Amar, R. Lan, C.T.G. Petit, S.W. Tao, J. Solid State Electrochem., 15 (2011) 1845-1860.[2] G.C. Xu, R.Q. Liu, J. Wang, Science in China Series B-Chemistry, 52 (2009) 1171-1175.[3] I.A. Amar, R. Lan, S.W. Tao, RSC Adv., 5 (2015) 38977-38983.[4] T. Matsui, T. Kukino, R. Kikuchi, K. Eguchi, Electrochem. Solid State Lett. 8 (2005) A256-A258. Figure 1

Temperature Dependence of Carbon Deposition in Ni-YSZ Cermet with Various Steam/Carbon Ratio

Solid oxide fuel cells (SOFCs) are one of promising power generation systems having high energy conversion efficiency. Although SOFCs have been already commercialized, there still exist technical challenges for their further widespread utilization, such as the improvement of durability and reliability. The carbon deposition on the anode is known as one of possible causes for the degradation of SOFCs. It may cause the deactivation of electrode catalysis, the obstruction of gas diffusion pass, the structural deformation, and, in the worst case, the structural destruction. The deformation or destruction of the anode can be a fatal problem for SOFCs because many of commercialized SOFC cells are mechanically supported by the anode. Thus, for improving the durability and reliability of SOFCs, carbon deposition behavior on the anode should be understood. In this work, the carbon deposition on the porous composite of nickel and yttria-stabilized zirconia (Ni-YSZ cermet), which is the most typical SOFC anode showing excellent electronic conductivity, catalytic activity, thermodynamic stability and mechanical property, was investigated. In our previous works [1], carbon deposition on the Ni-YSZ cermet was investigated under various kinds of hydrocarbon gases. In this study, the temperature dependence of the carbon deposition in the Ni-YSZ cermet was investigated under the exposure to methane-containing gas with various steam /carbon ratios, S/C. Ni-YSZ porous cermet was prepared by mixing NiO (NiO-FP, Sumitomo Metal Mining Co., LTD.) and 8 mol % YSZ (TZ8YS, Tosoh Corp.) with the ratio of Ni:8YSZ = 40:60 vol%. 30 vol% of polymethyl-methacrylate (PMMA, SSX-102, Sekisui Plastics Co., LTD.) was added to the NiO/YSZ mixture as a pore forming material. The mixed powder was molded into a disk shape, and pressed under 100 MPa of hydrostatic pressure. The disk was sintered in air at 1673 K for 3 hours. The pellet was cut into blocks of 2×2×2 mm. Specimens of Ni-YSZ cermet were obtained by reducing the blocks of NiO-YSZ in 100%H2at 1073 K for 5 hours. The porosity of the obtained Ni-YSZ cermet was about 35 %. Thermogravimetry measurements of Ni-YSZ cermet were carried out by TG-DTA (2000S，MAC-Science Co. Ltd.). The NiO-YSZ specimen was first heated at 1073 K in 5%H2–N2 for 1 hour for reduction, and was cooled down to room temperature. Then the atmosphere was switched to dry or moisturized 10%CH4-N2, and the weight change was measured when the temperature was heated up to 1273 K. After the measurement, the atmosphere was switched to pure N2, and temperature was decreased down to room temperature. Figure 1 shows the weight change and the weight change rate of the Ni-YSZ cermet during exposure to 10%CH4-N2 with S/C = 0.1 when the specimen was heated with the heating rate of 5 K‧min-1. The weight of the Ni-YSZ cermet started to change from low temperature, and slightly increased with temperature. The weight decreased once around 720 K. Above this temperature, the weight increased with temperature again, while the weight change rate showed a local maximum around 800 K. Above 873 K, the weight and the weight change rate monotonically increased with temperature. Thermogravimetry measurements were carried out also with various S/C, 0 (dry), 0.05, and 0.2. As results, the temperature showing the local maximum of the weight change rate increased with increasing S/C. This indicated that the local maximum of the weight change rate was related to reactions involving steam. According to the thermodynamic calculation of equilibrium composition of chemical species in the CH4-H2O atmosphere [2], carbon deposition become significant with increasing temperature. This means that the characteristic behavior of the weight change and the weight change rate observed around 720 and 800 K cannot be simply explained thermodynamically, and kinetic effects, such as catalytic activities of Ni and side reactions by water vapor, should be considered. In the presentation, further detailed results of thermogravimetry measurements as well as analysis of deposited carbon will be given. [1] T. Nakamura, N. Ohmura, K. Yashiro, K. Amezawa, Electrochem. Soc. Trans., 57(1)(2013) 1539. [2] The Thermodynamic Database MALT for Windows; Kagaku Gijutsu Sha, http://www.kagaku.com/malt. Figure 1

Copper-Based Metal-Organic Porous Materials for CO2 Electrocatalytic Reduction to Alcohols.

The electrocatalytic reduction of CO2 has been investigated using four Cu-based metal-organic porous materials supported on gas diffusion electrodes, namely, (1) HKUST-1 metal-organic framework (MOF), [Cu3 (μ6 -C9 H3 O6 )2 ]n ; (2) CuAdeAce MOF, [Cu3 (μ3 -C5 H4 N5 )2 ]n ; (3) CuDTA mesoporous metal-organic aerogel (MOA), [Cu(μ-C2 H2 N2 S2 )]n ; and (4) CuZnDTA MOA, [Cu0.6 Zn0.4 (μ-C2 H2 N2 S2 )]n . The electrodes show relatively high surface areas, accessibilities, and exposure of the Cu catalytic centers as well as favorable electrocatalytic CO2 reduction performance, that is, they have a high efficiency for the production of methanol and ethanol in the liquid phase. The maximum cumulative Faradaic efficiencies for CO2 conversion at HKUST-1-, CuAdeAce-, CuDTA-, and CuZnDTA-based electrodes are 15.9, 1.2, 6, and 9.9 %, respectively, at a current density of 10 mA cm-2 , an electrolyte-flow/area ratio of 3 mL min cm-2 , and a gas-flow/area ratio of 20 mL min cm-2 . We can correlate these observations with the structural features of the electrodes. Furthermore, HKUST-1- and CuZnDTA-based electrodes show stable electrocatalytic performance for 17 and 12 h, respectively.

The Role of the Hydrogen Source on the Selective Production of γ-Valerolactone and 2-Methyltetrahydrofuran from Levulinic Acid.

A mechanistic study of the hydrogenation reaction of levulinic acid (LA) to 2-methyltetrahydrofuyran (MTHF) was performed using three different solvents under reactive H2 and inert N2 atmospheres. Under the applied reaction conditions, catalytic transfer hydrogenation and hydrogenation with molecular H2 were effective at producing high yields of γ-valerolactone. However, the conversion of this stable intermediate to MTHF required the combination of both hydrogen sources (the solvent and the H2 atmosphere) to achieve good yields. The reaction system with 2-propanol as solvent and Ni-Cu/Al2 O3 as catalyst allowed full conversion of LA and a MTHF yield of 80 % after 20 h reaction time at 250 °C and 40 bar of H2 (at room temperature). The system showed the same catalytic activity at LA feed concentrations of 5 and up to 30 wt%, and also when high acetone concentration at the beginning of the reaction were added, which confirmed the potential industrial applications of this solvent/catalyst system.

Continuous reduction of the oxide scale of hot-rolled steel strip in hydrogen

The continuous reduction in the oxide scale of hot-rolled steel strip in H2–N2 atmosphere was simulated in laboratory. Scale specimens were reduced in 20% H2–N2 or 50% H2–N2 atmosphere. The sample weight losses were measured after soaking at 550, 700 and 800°C. In both atmospheres, specimen reduced at 700°C showed the minimum weight loss after soaking for 240 s. At 700 and 800°C, higher hydrogen concentration accelerated the reaction in the beginning of soaking, but had little effect once the dense-reduced iron layer formed. While at 550°C, the reduced iron kept growing in porous structure and the weight loss rate increased significantly in higher H2 concentration.

The use of different types of reduced graphene oxide in the preparation of Fe-N-C electrocatalysts: capacitive behavior and oxygen reduction reaction activity in alkaline medium

Three different types of reduced graphene oxide (rGO) were prepared starting from graphite oxide (GO) produced with the Hummers’ method using three different exfoliation-reduction strategies: thermal annealing under N2 atmosphere at 700 °C, thermal annealing under H2–N2 (1:1 vol.) atmosphere at 500 °C and ultrasonication. Then, three non-noble metal catalysts (NNMC) for the oxygen reduction reaction (ORR) were synthesized using these three different rGO as carbon supports, by impregnation of a complex formed between Fe(II) ions and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) as source of nitrogen, followed by a pyrolysis at 800 °C. The physical-chemical properties of rGO and Fe-N/rGO catalysts were characterized by N2 physisorption, XRD, XPS, SEM, and EDX. The capacitive behavior and the ORR activity of rGO and Fe-N/rGO catalysts were measured in alkaline conditions by cyclic voltammetry (CV) and rotating disk electrode (RDE), respectively. The three different reduction-exfoliation methods used for the rGO preparation influenced the physical-chemical properties, as well as the capacitive currents and the ORR activity of both rGO and Fe-N/rGO. This provides an insight about which synthesis process could be the most convenient for the final application.

Synthesis of Ultrastable Ag Nanoplates/Polyethylenimine–Reduced Graphene Oxide and Its Application as a Versatile Electrochemical Sensor

Investigations on Ag nanostructures/reduced graphene oxide composites have been frequently reported, yet the morphology control of those loaded Ag nanocrystals is still challenging. We herein develop a facile method to grow triangular Ag nanoplates (AgP) on polyethylenimine-modified reduced graphene oxide (AgP/PEI-rGO). The AgP/PEI-rGO hybrids show unexpected high stability against chloride ions (Cl(-) ) and hydrogen peroxide (H2 O2 ), which is possibly due to the strong interaction between surface Ag atoms with the amine groups of PEI. In the chronoamperometry measurements for detecting H2 O2 , N2 H4 , and NaNO2 , the AgP/PEI-rGO hybrid shows very wide linear ranges (usually 10(-6) -10(-2) mol L(-1) for H2 O2 , N2 H4 , and NaNO2 ) and low detection limits (down to ≈1×10(-7) mol L(-1) ), which demonstrate the promising electrochemical sensor applications of these metal/graphene hybrids with well-defined morphologies and facets. In addition, this strategy could be extended to the deposition of other noble metals on rGO with controlled morphologies.