Hydrogen permeation on Al2O3-based nickel/cobalt composite membranes

Al₂O₃ was synthesized using the sol-gel process with aluminum isopropoxide as the precursor and primary distilled water as the solvent. Nickel and cobalt metal powders were used to increase the strength of the membranes. The Al₂O₃-based membranes were prepared using HPS following a mechanical alloying process. The phase transformation, thermal evolution, surface and cross-section morphology of Al₂O₃ and Al₂O₃-based membranes were characterized by XRD, TG-DTA and FE-SEM. The hydrogen permeation of Al₂O₃-based membranes was examined at 300–473 K under increasing pressure. Hydrogen permeation flux through an Al₂O₃-20wt%Co membrane was obtained to 2.36 mol m⁻² s⁻¹. Reaction enthalpy was calculated to 4.5 kJ/mol using a Van’t Hoff’s plot.     

Optical properties and thermal stability of pulsed-sputter-deposited AlxOy/Al/AlxOy multilayer absorber coatings

Spectrally selective Al_xO_y/Al/Al_xO_y multilayer absorber coatings were deposited on copper (Cu) and molybdenum (Mo) substrates using a pulsed sputtering system. The Al targets were sputtered using asymmetric bipolar-pulsed DC generators in Ar+O₂ and Ar plasmas to deposit an Al_xO_y/Al/Al_xO_y coating. The compositions and thicknesses of the individual component layers were optimized to achieve high solar absorptance (α=0.950-0.970) and low thermal emittance (ε=0.05-0.08). The X-ray diffraction data in thin film mode showed an amorphous structure of the Al_xO_y/Al/Al_xO_y coating. The X-ray photoelectron spectroscopy data of the Al_xO_y/Al/Al_xO_y multilayer absorber indicated that the Al_xO_y layers present in the coating were non-stoichiometric. The optical constants (n and k) of the multilayer absorber were determined from the spectroscopic ellipsometric data. Drude's free-electron model was used for generating the theoretical dispersion of optical constants for Al films, while the Tauc-Lorentz model was used for modeling optical properties of the dielectric Al_xO_y layers. In order to study the thermal stability of the Al_xO_y/Al/Al_xO_y coatings, they were subjected to heat treatment (in air and vacuum) at different temperatures and durations. The multilayer absorber deposited on Cu substrates exhibited high solar selectivity (α/ε) of 0.901/0.06 even after heat-treatment in air up to 400 °C for 2 h. At 450 °C, the solar selectivity decreased significantly on Cu substrates (e.g., α/ε=0.790/0.07). The coatings deposited on Mo substrates were thermally stable up to 800 °C in vacuum with a solar selectivity of 0.934/0.05. The structural stability of the absorber coatings heat treated in air (up to 400 °C) and vacuum (up to 800 °C) was confirmed by micro-Raman spectroscopy measurements. Studies on the accelerated aging tests suggested that the absorber coatings on Cu were stable in air up to 75 h at 300 °C and the service lifetime of the multilayer absorber was predicted to be more than 25 years. Further, the activation energy for the degradation of the multilayer absorber heat treated for longer durations in air is of the order of 64 kJ/mol.     

A feasibility study of integrally colored Al–Si as a solar selective absorber

The solar selective properties of integrally colored Al–Si alloy (11.6 wt% Si) have been investigated. Optical measurements showed a continuous decrease of reflectance, i.e. an increase of absorptance, with increasing film thickness. A maximum solar absorption of 0.85 was achieved for Si–Al₂O₃ coatings thicker than 13 μm but such thick aluminum oxide coatings have very high thermal emittance.The reflectance of the Si–Al₂O₃ coated aluminum could be understood from a four flux radiative transfer theory. Using this theory the optical performance of the coating as a solar absorber was modeled for different size and volume fractions of silicon particles and coating thicknesses. A solar absorptance of just 0.90 can be achieved from a 10 μm thick coating of about 0.3 volume fraction of silicon. For thinner coatings (1 μm) the solar absorptance was only 0.70 for the same volume fraction.     

Cooling of minichannel heat sink using nanofluids

Nanofluids contain a small fraction of solid nanoparticles in base fluids. Nanofluids cooled small channel heat sinks, have been anticipated to be an excellent heat dissipation method for the next generation electronic devices. In this study, nanofluids are used with different volume fractions of nanoparticles as a coolant for the minichannel. Al₂O₃–water nanofluid and TiO₂–water nanofluid were tested for the copper minichannel heat sink, with the bottom of 20 × 20 mm laminar flow as a coolant, through hydraulic diameters. The result showed that adding Al₂O₃ nanoparticles to water at 4% of volume fractions, enhanced the thermal conductivity by 11.98% and by dispersing TiO₂ to the base fluid, was 9.97%. It was found that using nanofluid such as Al₂O₃–water instead of water, improved the cooling by 2.95% to 17.32% and by using TiO₂–water, 1.88% to 16.53% was achieved. The highest pumping power by using Al₂O₃–water and TiO₂–water at 4 vol.% and 0.1 m/s was 0.000552 W and at 4 vol.% and 1.5 m/s was 0.12437 W.     

Oxidative steam reforming of methanol over CuO/ZnO/CeO2/ZrO2/Al2O3 catalysts

The composition (CuO/ZnO/Al₂O₃ = 30/60/10) of a commercial catalyst G66B was used as a reference for designing CuO/ZnO/CeO₂/ZrO₂/Al₂O₃ catalysts for the oxidative (or combined) steam reforming of methanol (OSRM). The effects of Al₂O₃, CeO₂ and ZrO₂ on the OSRM reaction were clearly identified. CeO₂, ZrO₂ and Al₂O₃ all promoted the dispersions of CuO and ZnO in CuO/ZnO/CeO₂/ZrO₂/Al₂O₃ catalysts. Aluminum oxide lowered the reducibility of the catalyst, and weakened the OSRM reaction. Cerium oxide increased the reducibility of the catalyst, but weakened the reaction. Zirconium oxide improved the reducibility of the catalyst, and promoted the reaction. A lower CuO/ZnO ratio of the catalyst was associated with greater promotion of ZrO₂. The critical CuO/ZnO ratio for the promotion of ZrO₂ was approximately 0.75–0.8. Introducing of ZrO₂ into CuO/ZnO/Al₂O₃ also improved the stability of the catalyst. Although Al₂O₃ inhibited the OSRM reaction, a certain amount of it was required to ensure the stability and the mechanical strength of the catalysts.     

Evaluation of Ni/Y2O3/Al2O3 catalysts for hydrogen production by autothermal reforming of methane

Ni/xY₂O₃–Al₂O₃ (x = 5, 10, 15, 20 wt%) catalysts were prepared by sequential impregnation synthesis. The catalytic performance for the autothermal reforming of methane was evaluated and compared with Ni/γ-Al₂O₃ catalyst. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H₂-temperature programmed reduction techniques (TPR). The decrease of nickel particle size and the change of reducibility were found with Y modification. The CH₄ conversion increased with elevating levels of Y₂O₃ from 5% to 10%, then decreased with Y content from 10% to 20%. Ni/xY₂O₃–Al₂O₃ catalysts maintained high activity after 24 h on stream, while Ni/Al₂O₃ had a significant deactivation. The characterization of spent catalysts indicated that the addition of Y retarded Ni sintering and decreased the amount of coke.     

Hydrogen production by steam reforming of dimethyl ether over ZnO–Al2O3 bi-functional catalyst

A series of ZnO–Al₂O₃ catalysts with various ZnO/(ZnO + Al₂O₃) molar ratios have been developed for hydrogen production by dimethyl ether (DME) steam reforming within microchannel reactor. The catalysts were characterized by N₂ adsorption-desorption, X-ray diffraction and temperature programmed desorption of NH₃. It was found that the catalytic activity was strongly dependent on the catalyst composition. The overall DME reforming rate was maximized over the catalyst with ZnO/(ZnO + Al₂O₃) molar ratio of 0.4, and the highest H₂ space time yield was 315 mol h⁻¹·kg_cat⁻¹ at 460 °C. A bi-functional mechanism involving catalytic active site coupling has been proposed to account for the phenomena observed. An optimized bi-functional DME reforming catalyst should accommodate the acid sites and methanol steam reforming sites with a proper balance to promote DME steam reforming, whereas all undesired reactions should be impeded without sacrificing activity. This work suggests that an appropriate catalyst composition is mandatory for preparing good-performance and inexpensive ZnO–Al₂O₃ catalysts for the sustainable conversion of DME into H₂-rich reformate.     

Hydroprocessing of Jatropha oil over NiMoCe/Al2O3 catalyst

The non-sulfided NiMoCe/Al₂O₃ catalyst was developed to produce green diesel from the hydroprocessing of Jatropha oil. The NiMoCe/Al₂O₃ catalysts were prepared by impregnation and characterized by N₂-BET, SEM, XRD and TPD-H_ads techniques. The straight chain alkanes ranging from C15 to C18 were the main components in product oil. The maximum yield of C15-C18 alkanes of 80%, selectivity of 90% and conversion of 89% were obtained at 370 °C, 3.5 MPa and 0.9 h⁻¹. Influence of reaction temperature (280–400 °C) and reaction time (10–163 h) on the composition of product oil were discussed. The experimental results demonstrated that a suitable amount of metal Ce doping on the NiMo/Al₂O₃ catalyst presented stable catalytic performance and enhanced Jatropha oil conversion as well as C15-C18 fraction selectivity.     

Al2O3-coated nanoporous TiO2 electrode for solid-state dye-sensitized solar cell

This paper reports the preparation of a core-shell nanoporous electrode consisting of an inner TiO₂ porous matrix and a thin overlayer of Al₂O₃, and its application for solid-state dye-sensitized solar cell using p-CuI as hole conductor. Al₂O₃ overlayer was coated onto TiO₂ porous film by the surface sol–gel process. The role of Al₂O₃ layer thickness on the cell performance was investigated. The solar cells fabricated from Al₂O₃-coated electrodes showed superior performance to the bare TiO₂ electrode. Under illumination of AM 1.5 simulated sunlight (89 mW/cm²), a ca. 0.19 nm Al₂O₃ overlayer increased the photo-to-electric conversion efficiency from 1.94% to 2.59%.     

Photocatalytic hydrogen production from aqueous methanol solution with CuO/Al2O3/TiO2 nanocomposite

The photocatalytic hydrogen production from aqueous methanol solution was investigated with ZnO/TiO₂, SnO/TiO₂, CuO/TiO₂, Al₂O₃/TiO₂ and CuO/Al₂O₃/TiO₂ nanocomposites. A mechanical mixing method, followed by the solid-state reaction at elevated temperature, was used for the preparation of nanocomposite photocatalyst. Among these nanocomposite photocatalysts, the maximal photocatalytic hydrogen production was observed with CuO/Al₂O₃/TiO₂ nanocomposites. A variety of components of CuO/Al₂O₃/TiO₂ photocatalysts were tested for the enhancement of H₂ formation. The optimal component was 0.2 wt% CuO/0.3 wt% Al₂O₃/TiO₂. The activity exhibited approximately tenfold enhancement at the optimum loading, compared with that with pure P-25 TiO₂. Nano-sized TiO₂ photocatalytic hydrogen technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy.     

Nanocrystallites-forming hierarchical porous Ni/Al2O3–TiO2 catalyst for dehydrogenation of organic chemical hydrides

Dehydrogenation of organic chemical hydrides has been improved by reconstructing the catalyst in the form of hierarchical porous structure nanocatalyst, in which the economical Ni was adopted as catalytic component and nano Al₂O₃–TiO₂ hybrid composite as support. The Al₂O₃–TiO₂ composite was prepared by spontaneous self-assembly of nano Al₂O₃ and TiO₂ aggregates by hydrolysis of tetra-n-butyl-titanate under continuous agitation. The multi-scaled distribution of Al₂O₃–TiO₂ aggregates with hierarchy could be observed in dynamic light scattering spectrometer. The aggregates are comprised of nano-sized γ-Al₂O₃ and anatase TiO₂ crystallites with sizes of about 5 and 7 nm, respectively. The surface modulation by TiO₂ could be verified in FTIR Spectra. The migration of Ti species and crystallite growth were hindered by the Al₂O₃ skeleton and the hierarchical porous structure was sustained during the thermal related process. The multi-scaled distributed pores were confirmed by both TEM analysis and N₂ adsorption results. The results of dehydrogenation experiments showed that the hierarchical porous structure nano Ni/Al₂O₃–TiO₂ exhibited superior catalytic performance to Ni/Al₂O₃ with the optimum conversion of 99.9% at 400 °C, while the catalyst of Ni/Al₂O₃ exhibited only 16.5% under the same condition.     

Cathode having high rate performance for a secondary Li-ion cell surface-modified by aluminum oxide nanoparticles

In order to enhance the electrochemical properties, the spinel LiMn₂O₄ electrode surface was modified with amorphous Al₂O₃ nanoparticle as heterogeneous phase. LiMn₂O₄ was in preparation based on a conventional solid-state reaction. The LiMn₂O₄ procedure was soaked in aluminum tri 2-propoxide solution. The LiMn₂O₄ whose surface was modified by aluminum oxide was obtained through the heat treatment at 400 °C for 4 h. The Al₂O₃-modified LiMn₂O₄ electrode exhibits a capacity higher than that of the unmodified LiMn₂O₄ electrode. On the other hand, no variation was shown with open circuit potential and apparent chemical diffusion coefficient of Li ion for LiMn₂O₄ before and after the surface modification. The charge-transfer resistance of Al₂O₃-modified LiMn₂O₄ decreased significantly in comparison with the unmodified LiMn₂O₄. The improved charge-transfer kinetics was largely attributed to Al₂O₃ which plays an important role of increasing the chemical potential at the electrode/electrolyte interface.     

Quaternized poly(vinyl alcohol)/alumina composite polymer membranes for alkaline direct methanol fuel cells

The quaternized poly(vinyl alcohol)/alumina (designated as QPVA/Al₂O₃) nanocomposite polymer membrane was prepared by a solution casting method. The characteristic properties of the QPVA/Al₂O₃ nanocomposite polymer membranes were investigated using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), micro-Raman spectroscopy, and AC impedance method. Alkaline direct methanol fuel cell (ADMFC) comprised of the QPVA/Al₂O₃ nanocomposite polymer membrane were assembled and examined. Experimental results indicate that the DMFC employing a cheap non-perfluorinated (QPVA/Al₂O₃) nanocomposite polymer membrane shows excellent electrochemical performances. The peak power densities of the DMFC with 4 M KOH + 1 M CH₃OH, 2 M CH₃OH, and 4 M CH₃OH solutions are 28.33, 32.40, and 36.15 mW cm⁻², respectively, at room temperature and in ambient air. The QPVA/Al₂O₃ nanocomposite polymer membranes constitute a viable candidate for applications on alkaline DMFC.     

Production of hydrogen by methane catalytic decomposition over Ni–Cu–Fe/Al2O3 catalyst

Catalysts with high nickel concentrations 75%Ni–12%Cu/Al₂O₃, 70%Ni–10%Cu–10%Fe/Al₂O₃ were prepared by mechanochemical activation and their catalytic properties were studied in methane decomposition. It was shown that modification of the 75%Ni–12%Cu/Al₂O₃ catalyst with iron made it possible to increase optimal operating temperatures to 700–750 °C while maintaining excellent catalyst stability. The formation of finely dispersed Ni–Cu–Fe alloy particles makes the catalysts stable and capable of operating at 700–750 °C in methane decomposition to hydrogen and carbon nanofibers. The yield of carbon nanofibers on the modified 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst at 700–750 °C was 150–160 g/g. The developed hydrogen production method is also efficient when natural gas is used as the feedstock. An installation with a rotating reactor was developed for production of hydrogen and carbon nanofibers from natural gas. It was shown that the 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst could operate in this installation for a prolonged period of time. The hydrogen concentration at the reactor outlet exceeded 70 mol%.     

Study on pine biomass air and oxygen/steam gasification in the fixed bed gasifier

The pine biomass gasification under air and oxygen/steam atmosphere was experimentally studied in a fixed bed reactor. The effects of air flow, gasification temperature, oxygen concentration, steam flow and the catalytic cracking reaction temperature on production distribution were investigated. The results indicate that the H₂ content reaches the maximum at the gasification temperature 850 °C for a given air flow. Comparing with air-gasification atmosphere, the lower heating value (LHV) of produced syngas is higher (up to 8.76 MJ/Nm³) under oxygen-enriched gasification atmosphere. And the introduction of steam to the oxygen-enriched gasification leads to a higher H₂ content and LHV of produced synthesis gas. Additionally, the syngas content increases significantly with increasing catalytic cracking reaction temperature when Ni–Al₂O₃ catalyst was employed in catalytic cracking process. The results also reveal that the steam reforming reactions of methane and carbon dioxide are enhanced over Ni–Al₂O₃ catalyst. The effects of different loading of metal oxide additives to Ni–Al₂O₃ catalyst on the catalytic activity were discussed, and it is found that the Fe₂O₃/Ni–Al₂O₃ catalyst shows the best catalytic activity and the H₂ content achieves the maximum value of 39.21 vol.%.     

Optical properties of sol–gel deposited Al2O3 films

Highly transparent, uniform and corrosion resistant Al₂O₃ films were prepared on stainless-steel and quartz substrates by the sol–gel process from stable coating solutions using aluminum-sec-butoxide, Al(OBu^s)₃ as precursor, acetylacetone, AcAcH as chelating agent and nitric acid, HNO₃, as catalyzer. Films up to 1000 nm thick were prepared by multiple spin coating deposition, and were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), optical spectroscopy and micro Vickers hardness test. XRD of the film heat treated at 400°C showed that they had an amorphous structure. XPS confirmed that they were stoichiometric Al₂O₃. The refractive index (n) and extinction coefficient (k) were found to be n=1.56±0.01 and k=0.003±0.0002 at 600 nm, respectively. The surface microhardness and corrosion resistance investigations showed that Al₂O₃ films improved the surface properties of stainless-steel substrates.     

Electrochemical performance of LiCoO2 cathodes by surface modification using lanthanum aluminum garnet

LiCoO₂ particles were coated with various wt.% of lanthanum aluminum garnets (3LaAlO₃:Al₂O₃) by an in situ sol–gel process, followed by calcination at 1123 K for 12 h in air. X-ray diffraction (XRD) patterns confirmed the formation of a 3LaAlO₃:Al₂O₃ compound and the in situ sol–gel process synthesized 3LaAlO₃:Al₂O₃-coated LiCoO₂ was a single-phase hexagonal α-NaFeO₂-type structure of the core material without any modification. Scanning electron microscope (SEM) images revealed a modification of the surface of the cathode particles. Transmission electron microscope (TEM) images exposed that the surface of the core material was coated with a uniform compact layer of 3LaAlO₃:Al₂O₃, which had an average thickness of 40 nm. Galvanostatic cycling studies demonstrated that the 1.0 wt.% 3LaAlO₃:Al₂O₃-coated LiCoO₂ cathode showed excellent cycle stability of 182 cycles, which was much higher than the 38 cycles sustained by the pristine LiCoO₂ cathode material when it was charged at 4.4 V.     

Catalytic properties of Ag promoted ZnO/Al2O3 catalysts for hydrogen production by steam reforming of ethanol

Ag promoted ZnO/Al₂O₃ catalysts were prepared by using the incipient wetness impregnation method. The catalytic properties of steam reforming reaction for hydrogen production on the prepared catalysts were evaluated with H₂O:C₂H₅OH molar ratios of 3:1 at 450 °C and atmospheric pressure. Ag promoted ZnO/Al₂O₃ catalysts show higher SRE catalytic activity than ZnO/Al₂O₃ catalysts. H₂ and CH₃CHO are the major products on Ag promoted catalysts, and C₂H₄ is also produced probably due to acid sites on Al₂O₃. SRE mechanism on Ag promoted ZnO/Al₂O₃ catalysts, which contains C-C scission, is different from that on ZnO/Al₂O₃ catalysts. A method based on thermogravimetry (TG), differential scanning calorimetry (DSC) and mass spectrometry (MS) was used to analysis the coking behavior on catalyst surface. The surfaces of Ag promoted ZnO/Al₂O₃ catalysts show two different types of coking, and suffer higher coke deposition during the steam reforming reaction.     

Non-thermal plasma assisted synthesis and physicochemical characterizations of Co and Cu doped Ni/Al2O3 nanocatalysts used for dry reforming of methane

Ni/Al₂O₃ nanocatalysts doped with Co and Cu were prepared by co-impregnation and modified by non-thermal plasma. The nanocatalysts were characterized by XRD, FESEM, TEM, EDX dot-mapping, BET, FTIR, TGA-DTG, and XPS analysis. According to XRD and XPS results, good interaction between active phase and support can be observed in both Ni–Co/Al₂O₃ and Ni–Cu/Al₂O₃ nanocatalysts. A uniform morphology, high surface area, and well dispersed particles of active sites in Ni–Co/Al₂O₃ nanocatalyst were observed that shows the effect of cobalt in controlling Ni ensemble size. In contrast Ni–Cu/Al₂O₃ nanocatalyst had no homogenous dispersion of active phase due to sintering of copper particles. The activity measurements illustrated better Ni–Co/Al₂O₃ nanocatalyst activity in comparison to Ni/Al₂O₃ and Ni–Cu/Al₂O₃ in terms of CH₄ and CO₂ conversion. H₂ and CO yield were higher for Ni–Co/Al₂O₃ and higher H₂/Co ratio was obtained as well. Whereas Ni/Al₂O₃ and Ni–Co/Al₂O₃ did not experience deactivation, Ni–Cu/Al₂O₃ suffered from activity loss by ca. 22% and 16% for CH₄ and CO₂ conversion, respectively. Sintering most likely happened in Ni–Cu/Al₂O₃ nanocatalyst due to high temperature of calcination while cobalt by controlling the size of Ni particles, alternated the size of active sites to a size range in which carbon formation was suppressed. Ni/Al ratio from XPS analysis which signifies Ni dispersion on alumina support was 5.15, 9.16, and 6.35 for Ni/Al₂O₃, Ni–Co/Al₂O₃, and Ni–Cu/Al₂O₃ nanocatalysts respectively. The highest ratio of Ni/Al was for Ni–Co/Al₂O₃ nanocatalyst that shows the best coverage of support by Ni active phase in this nanocatalyst.     

In situ crack-healing behavior of Al2O3/SiC composite ceramics under static fatigue strength

A three-point bending (rectangular bar) specimen was made from sintered Al₂O₃/SiC composite ceramics and commercial Al₂O₃ material, upon which a semi-elliptical surface crack of 100 μm in diameter (aspect ratio ≒ 0.9) was introduced through an indentation method. The following materials were subjected to the following crack-healing treatment: Al₂O₃/SiC composite ceramics (under 1573 K temperature, 1 h crack-healing time) and monolithic Al₂O₃ (under 1373 K or 1723 K temperature, 1 h crack-healing time) designed to heal the crack samples.