Hydrogen production from bio-oil by chemical looping reforming

Hydrogen is a green energy carrier. Chemical looping reforming of biomass and its derivatives is a promising way for hydrogen production. However, the removal of carbon dioxide is costly and inefficient with the traditional chemical absorption methods. The objective of this article is to find a new material with low energy consumption and high capacity for carbon dioxide storage. A metal organic framework (MOF) material (e.g., CuBTC) was prepared using the hydrothermal synthesis method. The synthesized material was characterized by X-ray diffraction, ?196 °C N₂ adsorption/desorption isotherms, and thermogravimetry analysis to obtain its physical properties. Then BET, t-plot, and density functional theory (DFT) methods were used to acquire its specific surface area and pore textural properties. Its carbon dioxide adsorption capacity was evaluated using a micromeritics ASAP 2000 instrument. The results show that the decomposition temperature of the synthesized CuBTC material is 300 °C. Besides, high CO₂ adsorption capacity (4 mmol g^?1) and low N₂ adsorption capacity were obtained at 0 °C and atmospheric pressure. These results indicate that the synthesized MOF material has a high efficiency for CO₂ separation. From this study, it is expected that this MOF material could be used in adsorption and separation of carbon dioxide in chemical looping reforming process for hydrogen production in the near future.     

Influence of rhodium additive on hydrogen electrosorption in palladium-rich Pd–Rh alloys

Hydrogen electrosorption into Pd-rich (>80 at.% Pd in the bulk) Pd–Rh alloys has been studied in acidic solutions (0.5 M H₂SO₄) using cyclic voltammetry and chronoamperometry. The influence of temperature (in the range between 283 and 328 K), electrode potential and alloy bulk composition on hydrogen electrosorption properties of Pd–Rh alloys is presented. It has been found that the additive of Rh to Pd–Rh alloys increases the maximum hydrogen solubility (for Rh bulk content below 10 at.%), decreases the potential of absorbed hydrogen oxidation peak and decreases the potential of the α → β phase transition. Increasing temperature decreases the potential of absorbed hydrogen oxidation peak, the maximum hydrogen solubility, and the potential of the α → β phase transition. The amounts of electrosorbed hydrogen for α- and β-phase boundaries, i.e., α_max and β_min, have been determined from the integration of the initial parts of current–time responses in hydrogen absorption and desorption processes. The H/M ratio corresponding to α_max increases with increasing Rh content, while for β_min a maximum of H/M ratio is observed for the alloys containing ca. 95% Rh.

     

Electrocatalysis on binary alloys: II. Oxidation of molecular hydrogen on supported Pt+Ru alloys

The electrocatalytic properties of Pt+Ru alloys supported on graphitized carbon have been studied using oxide-free metal alloys that have been well characterized for phase identification, specific metal surface area, and surface composition. The CO tolerance of the Pt+Ru alloys for the oxidation of CO contaminated hydrogen in hot concentrated H₃PO₄ increases monotonically with Ru content of the surface and is a direct result of a decreasing coverage of the alloy by adsorbed CO. Furthermore, the strength of bonding of adsorbed CO with the metal surface decreases dramatically with increasing Ru content in the surface. The absolute activity of Pt+Ru alloys for the oxidation of CO contaminated hydrogen is a complex function of temperature and electrode potential. At 160°C, pure Pt is the most active catalyst at all potentials, but at temperatures lower than 120°C the reaction-limiting current for pure Ru exceeds that of pure Pt. At any temperature from 110–160°C or any electrode potential from 0–0.3V (HE), the variation of electrocatalytic activity with alloy composition indicates only dilution of the activity of the more active component.     

Photocatalytic Degradation of 2-Propanol and Phenol Using Au Loaded MnWO4 Nanorod Under Visible Light Irradiation

Single crystalline MnWO₄ nanorod has been prepared by low temperature hydrothermal reaction at 180 °C. The prepared MnWO₄ possesses band gap of 2.63 eV. Photochemical decomposition method has been followed to disperse Au nanoparticles onto MnWO₄ nanorod. The prepared Au loaded MnWO₄ nanorod demonstrated greatly enhanced photocatalytic activity in decomposing 2-propanol and evolving CO₂ in gas phase and phenol in aqueous phase compared to bare MnWO₄ and commercial TiO₂ nanoparticles (Degussa P25) under visible light (λ ≥ 420 nm) irradiation. The Au loading was optimized to 3.79 wt% for the highest efficiency. The enhanced photocatalytic activity originates from the absorption of visible light by MnWO₄ as well as the introduction of nanoparticulate Au on the surface of MnWO₄ as cocatalyst to impede the recombination of photogenerated charge-carriers.     

The influence of processing parameters on the fabrication of Si3N4 wires

Silicon nitride (Si₃N₄) wires have been prepared by means of carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine decomposed saccharose. The influence of temperature of reaction and mass ratio of carbon to silicon $ \left( \frac{C}{Si} \right) $ on the synthesis of Si₃N₄ wires were studied. The presence of nitrogen gas in the pores of gel at high temperature starts the CTRN reaction leading to the formation of Si₃N₄ wires. The results show that the Si₃N₄ was fully formed with two kinds of morphologies including globular and wire with a width of 100–500 nm and length of several microns at sintering temperature of 1,400 °C by employing the mass ratio of $ \frac{C}{Si} \; = \;0.5 $ . The infrared adsorption of the wires exhibits absorption bands related to the absorption peaks of Si–N bond of Si₃N₄. The thermal analysis results reveal that carbothermal nitridation reaction was completed at temperature of 1,400 °C.     

Improved electrochemical performance of nano-crystalline Li2FeSiO4/C cathode material prepared by the optimization of sintering temperature

Li₂FeSiO₄/C cathode materials have been prepared using the conventional solid-state method by varying the sintering temperature (650 °C, 700 °C and 750 °C), and the structure and electrochemical performance of Li₂FeSiO₄/C materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, respectively. The results show that Li₂FeSiO₄ nano-crystals with a diameter of about 6–8 nm are inbedded in the amorphous carbon, and the Li₂FeSiO₄/C material obtained at 700 °C exhibits an initial discharge capacity of 195 mA?h g^?1 at 1/16 C in the potential range of 1.5–4.8 V. The excellent electrochemical performance of Li₂FeSiO₄/C attributes to the improvement of conductivity and reduction of impurity by the optimization of the sintering temperature.     

Photo-oxidation of poly(vinyl chloride)

The photo-oxidation of PVC has been studied over the temperature range 30–150°C. Initiation with ultraviolet (2537A) radiation has been correlated with the presence of minute amounts of ozone. The contribution of atomic oxygen and singlet oxygen (¹Δ_g) molecules to the initiation mechanism is discussed. The β-chloroketones probably formed in the photo-oxidation of PVC, decomposed according to a Norrish type I reaction without loss of chlorine atoms. The gaseous products of the photo-oxidation of PVC at 30°C were carbon dioxide, carbon monoxide, hydrogen, and methane. Hydrogen chloride was obtained only when PVC was heated at high temperatures. When PVC was photo-oxidized and then heated at high temperature, benzene was obtained in addition to hydrogen chloride. The gaseous products from the photo-oxidations of model compounds, such as 4-chloro-2-butanone and 2,4-dichloropentane, were also compared with those from PVC. Hydrogen chloride was detected only after photo-oxidation at temperatures of 25°C or higher. Therefore, it was concluded that hydrogen chloride is mainly a product of thermal decomposition. Since unsaturation was not observed in photo-oxidized PVC films, the cause of discoloration is unclear. When PVC was modified by stabilizers or additives, the oxidative degradation was further complicated by side reactions with the additives.     

Mechanical and dielectric absorption of poly(vinyl chloride) and some related polymers

The mechanical and dielectric low temperature absorptions of poly(vinyl chloride) (PVC) and several modified PVC's have been studied over the temperature range from ?60 to +60°C. with some tests extending to ?150°C. and others to +170°C. The results indicate that the low-temperature absorption near ?50°C (β₂ absorption) decreases in intensity with chlorination, while the absorption at a higher temperature near 0°C (β₁ absorption) decreases in intensity with hydrogenation. The apparent activation energies of the β₁ and β₂ absorptions were calculated to be 16 kcal/mole and 10.7 kcal/mole, respectively. Besides, the β₂ absorption markedly decreases in intensity with addition of plasticizer, while the intensity of β₁ absorption is not much affected by increasing plasticizer content. From these results, the β₁ and β₂ processes are concluded to be the results of molecular motion in crystalline and amorphous region in PVC, respectively. For samples of reduced Cl content, another low-temperature absorption was located near ?120°C (γ absorption) and attributed to the presence of short sequences of ethylene units. It has also been observed that the temperature location of the high temperature absorption near 100°C (α absorption) shifts linearly to higher temperature with increasing chlorine content and to lower temperature with increasing hydrogen content.     

Surface characteristics and corrosion resistance of sol–gel derived CaO–P2O5–SrO–Na2O bioglass–ceramic coated Mg alloy by different heat-treatment temperatures

To improve the initial corrosion resistance and then make the degradation rate of magnesium alloys to meet the biomedical application, crack-free CaO–P₂O₅–SrO–Na₂O bioglass-ceramic coatings were synthesized on AZ31 magnesium alloy substrates using a sol–gel dip-coating technique followed by a heat-treatment in the temperature range of 400–500 °C. The effects of heat-treatment on the phase constituents, surface characteristics and corrosion resistances of the coatings were investigated. It was shown that the crystallization of Ca₂P₂O₇ occurred after the glass was treated at 400 °C. As the temperature increased from 400 °C to 450 °C, besides main phase Ca₂P₂O₇, β-Ca(PO₃)₂ and Ca₄P₆O₁₉ were identified as minor crystal phases in the glass–ceramic. No new phase was detected with the temperature increasing to 500 °C except for the further crystallization. Meanwhile, the water contact angles of the coatings decreased with the increase of heat-treatment temperature due to the great crystallization. The corrosion resistances of the coated magnesium alloys were studied by electrochemical corrosion techniques in the simulated body fluid. The results revealed that the coating heat-treated at 400 °C exhibited superior corrosion resistance because of less crystallization, suggesting that the calcium phosphate bioglass–ceramic coating can provide effective protection for magnesium alloy substrate to control its initial degradation in vivo and maintain the desired mechanical properties.     

Preparation and Catalytic Activity of a Novel Nanocrystalline ZrO2@C Composite for Hydrogen Storage in NaAlH4

Sodium alanate (NaAlH₄) has attracted intense interest as a prototypical high‐density hydrogen‐storage material. However, poor reversibility and slow kinetics limit its practical applications. Herein, a nanocrystalline ZrO₂@C catalyst was synthesized by using Uio‐66(Zr) as a precursor and furfuryl alcohol (FA) as a carbon source. The as‐synthesized ZrO₂@C exhibits good catalytic activity for the dehydrogenation and hydrogenation of NaAlH₄. The NaAlH₄‐7 wt % ZrO₂@C sample released hydrogen starting from 126 °C and reabsorbed it starting from 54 °C, and these temperatures are lower by 71 and 36 °C, respectively, relative to pristine NaAlH₄. At 160 °C, approximately 5.0 wt % of hydrogen was released from the NaAlH₄‐7 wt % ZrO₂@C sample within 250 min, and the dehydrogenation product reabsorbed approximately 4.9 wt % within 35 min at 140 °C and 100 bar of hydrogen. The catalytic function of the Zr‐based active species is believed to contribute to the significantly reduced operating temperatures and enhanced kinetics.     

Microwave-Assisted Hydrothermal Preparation, Characterization and Photocatalytic Properties of a Chrysanthemum-Shaped ZnWO4 Photocatalyst

A novel chrysanthemum-shaped monocline ZnWO₄ photocatalyst was synthesized by microwave-assisted hydrothermal method with Na₂WO₄·2H₂O and Zn(NO₃)₂·6H₂O as raw materials at different reaction temperatures. The prepared ZnWO₄ photocatalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy, Photoluminescence spectrum (PL) and UV–Vis absorption spectrum (UV–Vis). The photocatalytic property of the prepared chrysanthemum-shaped monocline ZnWO₄ photocatalyst was evaluated by the degradation of Rhodamine B (RhB) in aqueous solution. The effects of reaction temperature on the photocatalytic degradation efficiency of RhB were investigated. The results indicated that the chrysanthemum-shaped monocline ZnWO₄ photocatalyst is prepared by foliated powders with the sizes of about 30 nm and 500 nm respectively at 160 and 220 °C. The PL relative intensity of prepared ZnWO₄ photocatalyst is apparently intensifying with increasing temperature. The photocatalytic property decreases with the increasing recombination probability of the excited electrons and holes. The chrysanthemum-shaped monocline ZnWO₄ photocatalyst prepared at 160 °C possesses the best photocatalytic property, and the degradation efficiency of RhB at 180 min UV-light irradiation is achieved 75 %. The ZnWO₄ has good reusability property on degradation of RhB and the degradation rate is still higher than 65 % after three cycles.     

Hydrogen sorption–desorption studies on ZrCo–hydrogen system

The ZrCo–H₂ system was investigated in this study owing to its importance as a suitable candidate material for storage, supply, and recovery of hydrogen isotopes. Desorption hydrogen pressure-composition isotherms were generated at six different temperatures in the range of 524–624 K. A van’t Hoff plot was constructed using the plateau pressure data of each pressure-composition isotherms and the thermodynamic parameters were calculated for the hydrogen desorption reaction of ZrCo hydride. The enthalpy and entropy change for the desorption of hydrogen were found to be 83.7 ± 3.9 kJ mol^?1 H₂ and 122 ± 4 J mol^?1 H₂ K^?1, respectively. Hydrogen absorption kinetics of ZrCo–H₂ system was studied at four different temperatures in the range of 544–603 K and the activation energy for the absorption of hydrogen by ZrCo was found to be 120 ± 5 kJ mol^?1 H₂ by fitting kinetic data into suitable kinetic model equation.     

The surface oxidation behavior of Ni–45.16%Ti shape memory alloys at different temperatures

The isothermal oxidation behavior of Ni–45.16%Ti (composition in atomic percent) alloy was investigated by thermogravimetric analysis, and differential scanning calorimeter (DSC) methods. It was found that Ni-rich NiTi alloy exhibits a different oxidation behavior at temperatures above 400 °C in oxygen atmosphere. The alloy was exposed to oxygen atmosphere isothermally, i.e., between 400 and 800 °C, for 1 h. A gravimetric method was used to determine the oxidation kinetics and it was seen that the oxidation constant increases significantly with isothermal temperature. The activation energy of oxidation reaction for NiTi alloy was determined to be 65.47 kJ mol^?1. According to DSC measurements, the transformation temperature of alloy (M _s, M _f, A _s and A _f) was increased and also R phase disappeared above 500 °C. The formal oxides were determined by means of SEM–EDX measurements and obtained oxides are TiO and TiO₂ oxides.     

Synthesis and characterization of Co2+: MgAl2O4 nanocrystal

Nanocrystalline Co²⁺-doped magnesium aluminate spinel (MgAl₂O₄) has been synthesized for the first time from aqueous solution of metal nitrates containing citric acid as chelating agent by a sol-gel method. The gel was heat-treated at temperatures ranging from 710°C to 1000°C. The heated powder samples were characterized by X-ray diffraction analysis (XRD), transmission electron microscope (TEM), infrared (IR) and absorption spectroscopy. The results showed that the homogeneous nanocrystalline Co²⁺: MgAl₂O₄ could be obtained at the low temperature of 710°C. The optimal temperature is about 900°C and the average size of the powder grains is 50 nm or so. In the absorption spectrum, a broad absorption band from 1200 nm to 1600 nm was found, which indicated the existence of Co²⁺ in the tetrahedral sites because of the ⁴A₂(⁴F) → ⁴T(⁴F) transition of Co²⁺.     

Thermodynamic properties of LuCo3 hydrides

Hydrogen desorption isotherms were measured in the system LuCo₃H_x for [0 ⩽ x ⩽ 3.6 at temperatures of 0, 20, 40, 60 and 80°C. Pressure plateaux on the isotherms indicate the existence of two hydride phases in addition to the hydrogen-saturated metal α phase. The α and β phases exist over very narrow ranges of hydrogen concentration. At 20°C the plateau pressures are 647 Torr and 4202 Torr respectively, and the heats of absorption are −8.80 kcal (mol H₂)⁻¹ and −7.555 kcal (mol H₂)⁻¹ respectively for the α and β phases. From the temperature dependence of the isotherms, the partial molar heats and entropies of absorption and the heats and entropies of formation have been calculated as a function of x. The 20°C isotherm is compared with those of the other rare earth-Co₃ hydrides.     

Electrochemical characteristics of platinum-based binary catalysts for middle-temperature hydrogen-air fuel cells with phosphoric acid electrolyte

The high-temperature synthesis based on commercial catalyst E-TEK (40% Pt) using cobalt, chromium, and iron organic precursors as well as d-metal salts yielded PtM (1:1) catalysts (PtCo, PtCr, PtMn, PtNi, PtFe, and PtV) for electroreduction of molecular oxygen in concentrated H₃PO₄ at the temperature of 160°C. The phase composition of the synthesized catalysts was studied by powder diffraction. The electrochemical measurements were carried out in 15 M H₃PO₄ at 20 and 160°C using a model gas diffusion electrode. An assumption was made that close charging curves recorded for synthesized PtM catalysts in both hydrogen and oxygen adsorption ranges were due to formation of the core-shell structure: alloy core and surface layers enriched with platinum. The Tafel curves of molecular oxygen reduction in 15 M H₃PO₄ at 160°C were characterized with the sole slope of 0.10 to 0.11 V. The catalytic activity in the range of potentials from 0.8 to 0.9 V (RHE) was shown approximately twice as that of pure platinum catalyst. The highest activity was recorded for PtCo and PtCr binary catalysts. Their use in middle-temperature hydrogen-air fuel cells with solid polymeric electrolyte based on polybenzimidazole doped with phosphoric acid enabled 2- to 3-fold decrease of the platinum share in the cathode.     

Nanosized bismuth titanate (Bi4Ti3O12) system drive through auto-combustion process by using suspension titania (TiO2)

Bismuth titanate (Bi₄Ti₃O₁₂) was developed by means of titanium oxide (TiO₂) suspension in auto-combustion process at 220 °C to get nanosized (20 ± 5 nm) bismuth titanate (Bi₄Ti₃O₁₂) powder. Complete piezoelectric phase (tetragonal) was obtained after calcination at 700 °C. Dilatometery of compacts was performed to find out sintering temperature. On the basis of shrinkage results, compacts were sintered at 750, 800, and 850 °C for 2 h. After sintering single phase was obtained with orthorhombic structure analyzed by X-ray diffraction and also investigated by Rietveld method. High-resolution scanning electron microscopy revealed that fine plate-like structure which is a characteristic of BIT powder can be obtained at 850 °C. Sintering results indicate that density and average grain size increase with the increasing temperature. A maximum of about 90 % of the theoretical density was achieved for the sintered product at 850 °C.     

A Synergy of ZnO and ZnWO4 in Composite Nanostructures Deduced from Optical Properties and Photocatalysis

ZnO/ZnWO₄ composite rod-like nanoparticles were synthesized by low-temperature soft solution method at 95 °C with different reaction times (1–120 h), in the presence of non-ionic copolymer surfactant Pluronic F68. Obtained nanoparticles had diameters in the range around 10 nm and length of 30 nm. Optical properties such as reflection and room temperature photoluminescence of obtained samples showed strong dependence on their crystallinity and composition. Photocatalytic activity of ZnO/ZnWO₄ nanopowders was checked using photodegradation of selected dyes as model system. Obtained results were correlated with specific surface area, particle sizes, crystallinity and ZnO/ZnWO₄ ratio of the samples. As crystallinity of ZnWO₄ component in the ZnO/ZnWO₄ increase, photocatalytic activity also increases. The main findings can be explained by charge transfer reactions that follow light absorption by ZnO and ZnWO₄ in nanocomposite.     

Dielectric and switching properties of a highly tilted AFLC material (S)-(+)-4-(1-methylheptyloxycarbonyl)-2,3-difluorophenyl 4′-[3-(2,2,3,3,4,4,4-heptafluorobutoxy)prop-1-oxy]biphenyl-4-carboxylate

Thermodynamic, dielectric, optical and switching parameters of a single-phase antiferroelectric (AF) liquid crystalline material (S)-(+)-4-(1-methylheptyloxycarbonyl)-2,3-difluorophenyl 4′-[3-(2,2,3,3,4,4,4-heptafluorobutoxy)prop-1-oxy]biphenyl-4-carboxylate have been studied. These studies show wide temperature range (~97.8°C–25.3°C) of AF SmC^*_A phase in the material. The dielectric studies have been carried out in the frequency range of 1 Hz–35 MHz under planar anchoring conditions of the molecules. The dielectric spectrum of the SmC^*_A phase exhibits three relaxation modes due to the collective as well as individual molecular processes. Relaxation frequencies of these modes lie in the range of kHz–MHz regions. Relative permittivity of the material (at 10 kHz) varies from ~8.8 at 98.8°C to 9.9 at 41.0°C. Maximum tilt of the molecule in the SmC^*_A phase is ~43°C. Spontaneous polarisation, switching time and rotational viscosity have also been determined. The maximum value of P_S is ~439 nC/cm² and switching time is the order of 1–5 millisecond, whereas viscosity is moderate.     

Thermal and magnetic properties of Ni51Mn28.5Ga19.5B magnetic-shape-memory alloy

Ni₅₁Mn_28.5Ga_19.5B magnetic shape-memory alloy was produced in Arc melter under vacuum. The crystal structure of the produced alloy was determined by using XRD. The XRD analysis results indicated the presence of two phases; namely the martensitic phase that the alloy was determined to display non-modulated martensitic phase and the gamma phase characteristics. DSC was used to determine the transformation temperature, the thermodynamic quantities of martensitic transformation and the activation energy in the Ni₅₁Mn_28.5Ga_19.5B alloy. The austenite transformation temperature and activation energy of transition were found as 46.92 °C and 303.12 kJ mol^?1 respectively. The 1 % presence of the boron element in the alloy was observed to play a significant role in the transition temperature as indicated by the comparison of the values obtained in this study with those available in the literature. The magnetic properties of this alloy were determined using the PPMS instrument. The magnetic saturation value was determined as 66 emu g^?1.