Preparation of dual-phase composite BaCe0.8Y0.2O3/Ce0.8Y0.2O2 and its application for hydrogen permeation

Dual-phase ceramic membranes composed of BaCe_0.8Y_0.2O₃ (BCY) and Ce_0.8Y_0.2O₂ (CYO) were successfully synthesized by solid state reaction method for hydrogen permeation. The influences of the BCY/CYO volume ratios on phase composition, microstructure, chemical stability and electrical property were investigated. The hydrogen permeation of the dual-phase composite was characterized as a function of temperature and feed side hydrogen partial pressure. The results showed that there was no reaction between the two constituent oxides observed under the preparation conditions. The dual-phase composite with different BCY/CYO volume ratios after sintering at 1550 °C exhibited dense structure, as well as good stability in 4% H₂/Ar, wet Ar and pure CO₂ atmosphere. The conductivity of the dual-phase composite increased with the content of CYO increasing and 30BCY–70CYO exhibited the highest total conductivity of 2.6×10⁻² S cm⁻¹ at 800 °C in 4% H₂/Ar. The hydrogen permeability of 30BCY–70CYO sample was improved as the temperature and the hydrogen partial pressure in feed gas increased. The hydrogen permeation flux of 1.7 μmol cm⁻² s⁻¹ was achieved at 850 °C.     

The performance of CNT as catalyst support on CO oxidation at low temperature

A carbon nanotube (CNT) was used as catalyst support impregnated with transition metal cobalt for CO oxidation at low temperature. Catalyst properties were analyzed by X-ray powder diffractometer (XRD), X-ray photoelectron spectrometer (XPS), and transmission electron microscope (TEM). Analytical results for TEM and XRD demonstrated that cobalt particles were highly dispersed on the carbon nanotube (20–30 nm) with nanosized cobalt particles (10–15 nm). These investigations indicated that Co/CNT generates about 99% of the high activity for CO conversion at 250 °C and thermally stability that is superior to Co/activated carbon (AC). The optimum reaction conditions for CO conversion were O₂ concentration 3%, operation temperature 250 °C, CO concentration 5000 ppm, and space velocity 156,000 h⁻¹. At 250 °C, CO may act as a reductant for NO reduction over Co/CNT in the presence of oxygen, whereas CO/NO = 2.5 showed that maximum NO reduction was 30%. Under H₂ rich conditions, the optimum reaction temperature for CO conversion was under 300 °C, and performance of CO₂ selectivity was better at 200 °C than 250 °C as the oxygen concentration increased.     

Optimization of desulphurization of Artvin–Yusufeli lignite with acidic hydrogen peroxide solutions

In this study in which the Taguchi method was used, the optimization of sulphur removal by H₂O₂/H₂SO₄ solutions was carried out over lignite with higher content of sulphur from Artvin/Yusufeli, Turkey. In experiments, the ranges of experimental parameters were between 0.25 and 6.0 mol L⁻¹ for H₂O₂ concentration, 0.25–4 mol L⁻¹ for H₂SO₄ concentration, 10–60 °C for reaction temperature, 0.01–0.08 g mL⁻¹ for solid-to-liquid ratio, 15–120 min for reaction time, 200–300 rpm for stirring speed and 710–120 μm for particle size. The optimum conditions for these parameters have found to be 60 °C of temperature, 0.06 g mL⁻¹ of solid-to-liquid ratio, 60 min of reaction time, 250 rpm of stirring speed and −250 + 180 μm of particle size.A statistical experimental arrangement, L₂₅(5⁶) was prepared to determine optimum sulphur removal and ash removal ratios. The obtained yields were 97.85% in removal of total sulphur, 56.54% in removal of pyritic sulphur, 21.33% in removal of organic sulphur and 61.52% in removal of ash. According to variance analysis, it was seen that all parameters were effective in removal of pyritic and total sulphur, reaction temperature, solid-to-liquid ratio, reaction time, stirring speed, H₂O₂ and H₂SO₄ concentrations in removal of organic sulphur, and other parameters except acid concentration in removal of ash.     

Hydrothermal gasification of Rosa Damascena residues: Gaseous and aqueous yields

The gasification of Rosa Damascena residues – by-products of the rose-oil industry – was investigated under hydrothermal conditions at 500 °C and 600 °C, 35–45 MPa pressure with a reaction time of 1 h. The experiments were performed in the absence and presence of catalysts of K₂CO₃ and trona in a batch type reactor. The composition of the gaseous and aqueous products was determined by gas chromatography and high performance liquid chromatography, respectively. H₂, CO₂ and CH₄ are the main gaseous products while carboxylic acids (formic acid, acetic acid, glycolic acid) are the main components found in the aqueous phase followed by furfurals, phenols, aldehyde and ketones. More gaseous products were obtained at the higher temperature of 600 °C. Adding catalyst was found to aid the conversion process but the effect was only slight. Rosa Damascena residues have the potential to be a useful source for H₂ production in the future.     

Preparation,characterization and performance of Pd/SiO2 catalyst for benzene catalytic hydrogenation

Palladium nanoparticles supported on silica were prepared by hydrazine reduction in aqueous medium at room temperature. They were characterized by XRD, TEM, EDX, H₂-adsorption, and H₂-TPD. The catalytic properties were evaluated in the gas-phase hydrogenation of benzene in the temperature range of 75–250 °C. Metal particles with a size range of 4.0–25.8 nm were obtained. The metal surface area and hydrogen storage increase with decreasing metal particle size. The H₂-TPD profiles exhibited a main peak appeared at 540 °C with two shoulders at lower (445 °C) and higher (605 °C) temperatures. These peaks were ascribed to strongly adsorbed hydrogen on the surface catalyst. The catalytic activity of the catalysts strongly depends on the metal loading. It increases with decreasing Pd loading. This is ascribed to metal surface area, which increases with decreasing Pd content.     

Study on the hydrothermal treatment of Shenhua coal

In this paper, the hydrothermal treatment of Shenhua coal was carried out under 0.1 MPa (initial pressure) nitrogen and different temperature. Effects of hydrothermal treatment on the structure and the hydro-liquefaction activity of Shenhua coal were investigated by the ultimate and proximate analyses, the FTIR measurements and TG analyses of hydrothermally treated coals, and the characterizations of extraction and swelling properties, and the batch hydro-liquefaction of treated coal were also carried out. The results indicate that hydrothermal treatment above 200 °C can increase the hydrogen content of treated coal and decrease the yield of volatiles and the content of ash, especially a large amount of CO and CH₄ are found in gas products obtained by the hydrothermal treatment above 250 °C. Hydrothermal treatment disrupts the weak covalent bond such as ether, ester and side-chain substituent by hydrolysis and pyrolysis, and changes the distribution of H-bond in coal. The swelling ratio and the Soxhlet extraction yield of treated coal decrease with the increase of hydrothermal treatment temperature. The conversion of liquefaction and the yield of CS₂/NMP mixed solvent extraction at ambient temperature are enhanced by hydrothermal treatment at 300 °C. Therefore hydrogen donation reactions and the rupture of non-covalent bond and weak covalent bonds present in the process of hydrothermal treatment resulting in the changes of structure and reactivity of Shenhua coal. The results show that the hydro-liquefaction activity of Shenhua coal can be improved by hydrothermal pretreatment between 250 °C and 300 °C.     

Pd-YSZ cermet membranes with self-repairing capability in extreme H2S conditions

A Pd-YSZ cermet membrane that performs coupled operations of hydrogen separation from a mixed-gas stream and simultaneous hydrogen production by non-galvanic water-splitting, and have high sulfur tolerance is fabricated. It is proved that in H₂S containing atmosphere the Pd-YSZ membrane has self-repairing capability, originating mainly from the conversion of Pd₄S back to metallic Pd and SO₂ by ambipolar-diffused oxygen obtained from water-splitting. The performance of membrane was analyzed at different temperatures in high H₂S containing (0–4000 ppm H₂S) mixed gas feed during the operation as a hydrogen separation membrane as well as during the coupled operation of hydrogen separation and hydrogen production. At 900 °C with the feed-stream having ≥2000 ppm H₂S, the hydrogen flux was severely affected due to the formation of some liquid phase of Pd₄S, resulting in the segregation of hydrogen permeating Pd-phase at the membrane surface. But at 800 °C, though the membrane was affected by the Pd₄S formation in high H₂S environment (up to 1200 ppm H₂S), its self-repairing capability and additional hydrogen production by water-splitting is capable of maintaining the hydrogen flux around ~1.24 cm³ (STP)/min.cm², a value expected by the same membrane while performing only the hydrogen separation function in H₂S-free environment.     

Synthetic coal chars for the elucidation of NO heterogeneous reduction mechanisms

In the present work, the mechanisms involved in NO–char heterogeneous reduction have been studied using a synthetic coal char (SC char) as carbon source. Another synthetic char (SN char) without nitrogen in its composition has also been employed in these studies. Isothermal reduction tests at different temperatures have been carried out. Two temperature regimes were considered: low temperature (T < 250 °C) where NO chemisorption takes place and high temperature (T > 250 °C) where NO–C reaction occurs. Step response experiments combining consecutive reaction stages with NO and ¹⁵NO were performed in order to determine the role of nitrogen surface complexes, C(N), in the reduction process. The results revealed N₂ and CO₂ to be the main reduction products under the experimental conditions employed in this work. NO chemisorption at lower temperatures results in N₂ emission and surface complexes (mainly oxygenated) formation, while char gasification by NO involves a direct NO attack on the char surface to form surface complexes. As a consequence of desorption of these complexes new sites of reaction are created.     

Characteristics of the mercury vapor removal from coal combustion flue gas by activated carbon using H2S

Removal of Hg⁰ vapor from the simulated coal combustion flue gases with a commercial activated carbon was investigated using H₂S. This method is based on the reaction of H₂S and Hg over the adsorbents. The Hg⁰ removal experiments were carried out in a conventional flow type packed bed reactor system in the temperature range of 80–150 °C using simulated flue gases having the composition of Hg⁰ (4.9 ppb), H₂S (0–20 ppm), SO₂ (0–487 ppm), CO₂ (10%), H₂O (0–15%), O₂ (0–5%), N₂ (balance gas). The following results were obtained: in the presence of both H₂S and SO₂, Hg removal was favored at lower temperatures (80–100 °C). At 150 °C, presence of O₂ was indispensable for Hg⁰ removal from H₂S–SO₂ flue gas system. It is suggested that the partial oxidation of H₂S with O₂ to elemental sulfur (H₂S+1/2O₂=S_ad+H₂O) and the Clause reaction (SO₂+2H₂S=3S_ad+2H₂O) may contribute to the Hg⁰ removal over activated carbon by the following reaction: S_ad+Hg=HgS. The formation of elemental sulfur on the activated carbon was confirmed by a visual observation.     

Hydrogasification characteristics of bituminous coals in an entrained-flow hydrogasifier

The characteristics of hydrogasification to generate substitute natural gas (SNG) by using various bituminous coals such as Alaska, Cyprus, Curragh, and Datong have been determined in an entrained-flow hydrogasifier (0.025 m I.D.×1 m high) with high pressure coal feeder and data acquisition system. The effects of reaction pressure (60–80 atm), reaction temperature (600–800 °C) and H₂/coal ratio (0.3–0.5) on composition of product gas and carbon conversion have been determined. The concentration of SNG and carbon conversion increased with an increasing of reaction pressure and temperature, but the carbon conversion and concentration of each bituminous coal were quite different because of different coal properties. Also the H₂/coal ratio affected the carbon conversion and the concentration of SNG.     

Low temperature catalytic steam gasification of HyperCoal to produce H2 and synthesis gas

HyperCoal is an ultra clean coal with ash content <0.05 wt%. Catalytic steam gasification of HyperCoal was carried out with K₂CO₃ at 775–650 °C for production of H₂ rich gas and synthesis gas. The catalytic gasification of HyperCoal showed nearly four times higher gasification rate than raw coal. The major gases evolved were H₂: 63 vol%, CO: 6 vol% and CO₂: 30 vol%. Catalyst was recycled for four times without any significant rate loss. The partial pressure of steam was varied from 0.5 atm to 0.05 atm in order to investigate the effect of steam pressure on H₂/CO ratio. The H₂/CO ratio decreased from 9.5 at 0.5 atm to 1.9 at 0.05 atm. No significant decrease in gasification rate was observed due to change in partial pressure of steam. Gasification rate decreased with decreasing temperature and become very slow at 650 °C. The preliminary results showed that HyperCoal, an ash less coal, could be a potential hydrocarbon resource for H₂ and synthesis gas production at low temperature by catalytic steam gasification process.     

Preparation and characterization of BaCe0.95Tb0.05O3−α hollow fibre membranes for hydrogen permeation

BaCe_0.95Tb_0.05O_3?α (BCTb) perovskite hollow fibre membranes were fabricated by spinning the slurry mixture containing 66.67 wt% BCTb powder, 6.67 wt% polyethersulphone (PESf) and 26.67 wt% N-methyl-2-pyrrolidone (NMP) followed by sintering at elevated temperatures. The influence of sintering temperature on the membrane properties was investigated in terms of crystal phase, morphology, porosity and mechanical strength. In order to obtain gas-tight hollow fibres with sufficient mechanical strength, the sintering temperature should be controlled between 1350 and 1450 °C. Hydrogen permeation through the BCTb hollow fibre membranes was carried out between 700 and 1000 °C using 50% H₂–He mixture as feed on the shell side and N₂ as sweep gas in the fibre lumen. The measured hydrogen permeation flux through the BCTb hollow fibre membranes reached up to 0.422 μmol cm^?2 s^?1 at 1000 °C when the flow rates of the H₂–He feed and the nitrogen sweep were 40 mL min^?1 and 30 mL min^?1, respectively.     

Improvement in hydrogen production from hard-shell nut residues by catalytic hydrothermal gasification

The hydrothermal gasification of some hard-shell nut residues (hazelnut, walnut and almond shells) was performed in a batch type reactor at temperature and pressure ranges of 300–600 °C and 88–405 bar, respectively. The biomass samples were converted into gaseous product (hydrogen, carbon dioxide, methane, carbon monoxide and C₂–C₄ compounds), aqueous product (carboxylic acids, furfurals, phenols, aldehydes and ketones) and solid products after hydrothermal gasification. Hydrogen production was improved by using natural mineral catalysts (Trona, Dolomite and Borax). The activity of selected natural mineral catalysts in hydrothermal gasification can be ordered as being Trona [Na₃(CO₃)(HCO₃)·2H₂O] > Borax [Na₂B₄O₇·10H₂O] > Dolomite [CaMg(CO₃)₂]. The most effective catalyst was found to be Trona at 600 °C leading enhancement in hydrogen yields (mol H₂/kg C in biomass) for hazelnut, walnut and almond shells as 82.4%, 74.1% and 42.4%, respectively.     

Production of hydrogen and MWCNTs by methane decomposition over catalysts originated from LaNiO3 perovskite

LaNiO₃ type perovskite was prepared by the “self-combustion” method and was used as catalyst precursor for the methane decomposition reaction at 600 and 700 °C. CH₄ conversion reaches 80% at 700 °C and 65% at 600 °C using pure CH₄. The yield of CNT and H₂ were 2.2 g_CNT g^?1 h^?1 and 8.2 L g^?1 h^?1 at 700 °C respectively after 4 h of reaction. When the reaction is prolonged to 22 h the catalytic activity decreases but the catalyst is still active, the production of hydrogen reaches 63.5 L (STP) per gram of catalyst and the production of MWCNT was equal to 17 g per gram of catalyst.Multi-wall carbon nanotubes were characterized by X-ray diffraction (XRD), surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Raman spectroscopy. TEM micrographs showed that MWCNT longer than 20 μm were formed with inner diameters ranging from 5 to 16 nm and outer diameters up to about 40 nm.The results obtained here clearly show that the use of the perovskite LaNiO₃ as catalytic precursor is very effective for the simultaneous production of carbon nanotubes and hydrogen.     

Impact of quenching process on the surface defect of titanium dioxide for hydrogen production from photocatalytic decomposition of water

Nanocrystalline titania was prepared by solvothermal reaction of titanium butoxide in toluene at 300 °C for 2 h. Thus obtained-powder was calcined at 300 °C in box furnace for 1 h and then quenched in various media at different temperature. The physiochemical properties of samples were investigated by using X-ray diffraction (XRD), nitrogen adsorption, CO₂-Temperature Programmed Desorption (CO₂-TPD), UV–visible scanning spectrophotometer, Transmission electron microscopy (TEM) and electron spin resonance spectroscopy (ESR) techniques. All physical properties such as phase, BET surface area and crystal size were not changed after quenching processes. While the CO₂-TPD and ESR results indicate the changing of Ti³⁺ contents on the surface of TiO₂ after quenching process. The amounts of Ti³⁺ increased as the quenching temperature decreased. Photocatalytic decomposition of water was carried out to evaluate the catalytic activity of quenched TiO₂. The activity of quenched-powder increased corresponding to the increasing of Ti³⁺ contents increased by following order: air at 77 K > air at RT > air at 373 K > 30 wt% H₂O₂ at RT = 30 wt% H₂O₂ at 373 K > H₂O at RT > H₂O at 373 K.     

Low temperature atomic layer deposition of SiO2 thin films using di-isopropylaminosilane and ozone

Silicon dioxide (SiO₂) films are deposited by atomic layer deposition (ALD) at low temperatures from 100 to 200 °C using di-isopropylaminosilane (SiH₃N(C₃H₇)₂, DIPAS) as the Si precursor and ozone as the reactant. The SiO₂ films exhibit saturated growth behavior confirming the ALD process, showing a growth rate of 1.2 Å/cycle at 150 °C, which increases to 2.3 Å/cycle at 250 °C. The activation energy of 0.24 eV, extracted from temperature range of 100–200 °C, corresponds to the reported energy barrier for reaction between DIPAS and surface –OH. The temperature dependence of the growth rate can be explained in terms of the coverage and chemical reactivity of the thermally activated precursor on the surface. The ALD-SiO₂ films deposited at 200 °C show properties such as refractive index, density, and roughness comparable to those of conventionally deposited SiO₂, as well as low leakage current and high breakdown field. The fraction of Si–O bond increases at the expense of Si–OH at higher deposition temperature.     

Chemical oxidation of residual carbon from ZnAl2O4 powders prepared by combustion synthesis

The removal of carbon residue from ZnAl₂O₄ nanopowders by annealing at 500–800 °C leads to a decrease of specific surface area from 228.1 m²/g to 47.6 m²/g. At the same time, the average crystallite size increased from 5.1 nm to 14.9 nm. In order to overcome these drawbacks, a new solution for removing the carbon residue has been suggested: chemical oxidation using hydrogen peroxide. In terms of carbon removal, a H₂O₂ treatment for 8 h at 107 °C proved to be equivalent to a heat treatment of 1 h at 600 °C. The benefits of chemical oxidation over thermal oxidation were obvious. The specific surface area was much larger (188.1 m²/g) in the case of the powder treated with H₂O₂. The average crystallite size (5.8 nm) of ZnAl₂O₄ powder treated with H₂O₂ was smaller than the crystallite size (8.2 nm) of the ZnAl₂O₄ powder annealed at 600 °C.     

Structural,thermal and electrical studies of a novel rubidium phosphite tellurate compound

Structural, thermal and electrical properties studies of rubidium phosphite tellurate, RbH(PO₃H)·Te(OH)₆, were performed. An endothermic peak, which reached a completion at about 315 °C accompanied with a weight loss of 4.6 wt.%, was attributed to dehydration. Four types of pellets were produced, namely pellets A, B, C and D. Pellet A was tested with platinum–carbon paper electrode, and pellets B, C and D were tested with gold electrodes. Both pellets A and B were studied from 113 °C to 317 °C for 135 h. Pellet C was first investigated from room temperature to 176 °C for 360 h. After cooling down to room temperature, a second measurement with pellet C was carried out under the same conditions as used for pellets A and B. Pellet D, on the other hand, was heated up to 450 °C, kept at that temperature for 2 h and then cooled down to room temperature prior to the conductivity measurements. It was observed that the conductivities of pellets A and B decreased to values of 5.2 × 10^?8 S cm^?1 and 6.6 × 10^?7 S cm^?1 at 317 °C, respectively, and an unexpected rise in the conductivity (9.89 × 10^?6 S cm^?1 at 317 °C) was seen with pellet C. Dehydration of RbH(PO₃H)·Te(OH)₆ might be responsible for this unexpected rise in the conductivity of pellet C. The monoprotic part RbH(PO₃H) of RbH(PO₃H)·Te(OH)₆ apparently became diprotic (Rb₂H₂P₂O₅) part of Rb₂H₂P₂O₅·[Te(OH)₆]₂ after dehydration. The measured conductivity of pellet D, which was dehydrated prior to the measurement, reached a value of 5.41 × 10^?5 S cm^?1 at 317 °C and showed a good stability over-each-run time and temperatures measurement up to 317 °C. The dehydrated compound, Rb₂H₂P₂O₅·[Te(OH)₆]₂, has also a higher hydrogen density relative to the starting compound, RbH(PO₃H)·Te(OH)₆. It is deduced that completion of the dehydration can be responsible for the unexpected rise in the conductivity of RbH(PO₃H)·Te(OH)₆. This unusual case is important for studies in solid acid proton conductors.     

Synthesis,characterization and sinterablity of 10 mol% Sm2O3-doped CeO2 nanopowders via carbonate precipitation

A carbonate coprecipitation method has been used for the facile synthesis of highly reactive 10 mol% Sm₂O₃-doped CeO₂ (20SDC) nanopowders, employing nitrates as the starting salts and ammonium hydrogen carbonate (AHC) as the precipitant. The AHC/RE³⁺ (RE = Ce + Sm) molar ratio (R) and the reaction temperature (T) affect significantly the final yield and precursor properties, including chemical composition and particle morphology. Suitable processing conditions are T = 60 °C and R = 5.0–10, under which precipitation is complete and the resultant precursors show ultrafine particle size, spherical particle shape, and good dispersion. Thus, the processed precursors are rare-earth carbonates with an approximate formula of Ce_0.8Sm_0.2(CO₃)_1.5·1.8H₂O, which directly yield oxide solid-solutions upon thermal decomposition at a low temperature of ∼440 °C. The 20SDC solid solution powders calcined at 700 °C show excellent reactivity and have been densified to ∼99% of the theoretical via pressureless sintering at a very low temperature of 1200 °C for 4 h.