Composite phenolic resin-based carbon molecular sieve membranes for gas separation

Composite carbon molecular sieve membranes (c-CMSM) were prepared from phenolic resin loaded with boehmite by a single dipping–drying–pyrolysis step. The composite membrane was analyzed by scanning electron microscopy, high resolution transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, mercury porosimetry, CO₂ adsorption and permeation experiments. It was produced a 2 μm thick composite uniform layer on top of a α-Al₂O₃ support. The composite top layer exhibited nanowires of Al₂O₃ 1–2 nm thick and 10–30 nm long well dispersed in a microporous carbon matrix. The micropores network accounted for 63% of the total pore volume (DR isotherm). The c-CMSM exhibited ideal O₂/N₂ and C₃H₆/C₃H₈ permselectivities of 5 and 15, respectively. The performance of the c-CMSM for pair C₃H₆/C₃H₈ was above the upper bound curve for polymeric membranes, making it a promising vehicle for olefin purification.     

Fixed- and fluidised-bed synthesis of coiled carbon fibres on an in situ generated H2S-modified Ni/Al2O3 catalyst from a NiSO4/Al2O3 precursor

NiSO₄/Al₂O₃ and NiO/Al₂O₃ catalyst precursors were formed by calcination of NiSO₄·6H₂O/Al₂O₃ at 500 and 800 °C, respectively. The catalyst precursor was reduced under H₂ and N₂ and then reacted under C₂H₂, H₂ and N₂ at 650 °C. Coiled carbon fibres were formed in fixed- and fluidised-bed reactors using the NiSO₄/Al₂O₃ catalyst precursor. Thermodynamic modelling using an infinite equilibrium stage construction predicted complete reduction of NiSO₄ to Ni and simultaneous H₂S formation occurs in both fixed- and fluidised-bed systems. XRD measurements confirmed that Ni was the only catalytically active crystalline species present at concentrations >0.5 wt.% (XRD detection limit) post-reduction, however XRF and XPS measurements additionally detected the presence of small quantities (<0.9 wt.% S) of S species. S is adsorbed onto the Ni surfaces during reduction when H₂S is released and dissociates on the Ni surface. Non-coiled carbon fibres produced on the Ni/Al₂O₃ catalyst formed from the NiO/Al₂O₃ precursor demonstrated that modification of Ni/Al₂O₃ with S is required for coiled carbon fibre synthesis.     

Carbon–Al2O3–Ag composite molecular sieve membranes for gas separation

Phenolic resins loaded with two different inorganic fillers (boehmite (γ-AlO(OH)) and silver (Ag)) were used to prepare composite carbon membranes. Polymer solutions containing γ-AlO(OH) and AgNO₃ were prepared and the effect of Ag on the transport properties of the composite membrane was evaluated. The polymer solutions were coated on α-Al₂O₃ tubes and carbonized in a single dipping-drying-pyrolysis step. After pyrolysis at 550 °C, γ-AlO(OH) yielded γ-Al₂O₃, and Ag agglomerated forming spherical nanoparticles of 30 nm in diameter. Ag loading enhanced the carbon membrane performance for several gas pairs of interest, especially for C₃H₆/C₃H₈ separation, where the C₃H₆/C₃H₈ permselectivity increased from a maximum of 15 to 38.     

3-D micro-ceramic components from hydrothermally processed carbon nanotube–boehmite powders by electrophoretic deposition

Boehmite/multi-wall carbon nanotube (MWCNT) composite powders were prepared by hydrothermal processing. Starting chemical of aluminum acetate powders (2Al(OH)(C₂H₃O₂)₂) and MWCNTs were mixed for the formation of stoichiometric boehmite powders in an attempt to synthesize MWCNT-reinforced boehmite nano-powders via hydrothermal synthesis at 200 °C for 2 h. Kinetically stable suspensions of MWCNT–boehmite composite powders were prepared and subsequently electrophoretic deposition (EPD) was applied to obtain complex shape products in the form of micro-gears. It is shown that the EPD technique is a powerful tool to manufacture small components in a short time. Detail TEM observations also indicated that hydrothermal processing provides an ideal environment to obtain homogeneous mixtures of MWCNT–boehmite powders due to effective surface functionalization of MWCNTs under hydrothermal conditions.     

Boehmite coating on θ-Al2O3 particles via a sol–gel route

θ-Al₂O₃ powders in slurry form were coated by boehmite nanoparticles prepared from alumina sol that consists of aluminum tri-sec-butoxide (Al(OC₄H₉)₃) as a precursor. The θ-Al₂O₃ powders presented an iso-electrical point (IEP) at pH ∼ 9.2, and formed stable suspensions without notable gravity settling at acidic conditions (pH 3–4). Boehmite nanoparticles with a mean particle size ca. 68 nm were derived from the hydrolysis of Al(OC₄H₉)₃ sol. Well-dispersed boehmite/θ-Al₂O₃ aqueous mixtures consisting of 3 and 9 wt.% of boehmite were then prepared by addition of θ-Al₂O₃ powder into the Al(OC₄H₉)₃ sol followed then by vigorous agitation at 90 °C and in a pH range 3–4. IR and particle-size measurement both revealed possible coating of boehmite on the θ-Al₂O₃ particles. From TEM observation, “thickness” of the boehmite layer did not vary much with the boehmite concentration. Agglomeration of the particles became nonetheless apparent as the boehmite concentration was increased. The boehmite coating on θ-Al₂O₃ surface inhibited grain growth during the θ- to α-phase transformation upon heating. Mean grain size of the boehmite-coated alumina was substantially smaller than that of the un-coated one.     

Catalytic steam reforming of ethane and propane over CeO2-doped Ni/Al2O3 at SOFC temperature: Improvement of resistance toward carbon formation by the redox property of doping CeO2

Ni/Al₂O₃ with the doping of CeO₂ was found to have useful activity to reform ethane and propane with steam under Solid Oxide Fuel Cells (SOFCs) conditions, 700-900 °C. CeO₂-doped Ni/Al₂O₃ with 14% ceria doping content showed the best reforming activity among those with the ceria content between 0 and 20%. The amount of carbon formation decreased with increasing Ce content. However, Ni was easily oxidized when more than 16% of ceria was doped. Compared to conventional Ni/Al₂O₃, 14%CeO₂-doped Ni/Al₂O₃ provides significantly higher reforming reactivity and resistance toward carbon deposition. These enhancements are mainly due to the influence of the redox properties of doped ceria. Regarding the temperature programmed reduction experiments (TPR-1), the redox properties and the oxygen storage capacity (OSC) for the catalysts increased with increasing Ce doping content. In addition, it was also proven in the present work that the redox of these catalysts are reversible, according to the temperature programmed oxidation (TPO) and the second time temperature programmed reduction (TPR-2) results.During the reforming process, in addition to the reactions on Ni surface, the gas-solid reactions between the gaseous components presented in the system (C₂H₆, C₃H₈, C₂H₄, CH₄, CO₂, CO, H₂O, and H₂) and the lattice oxygen (O_x) on ceria surface also take place. The reactions of adsorbed surface hydrocarbons with the lattice oxygen (O_x) on ceria surface (C_nH_m+O_x→nCO+m/2(H₂)+O_x−n) can prevent the formation of carbon species on Ni surface from hydrocarbons decomposition reaction (C_nH_m⇔nC+m/2H₂). Moreover, the formation of carbon via Boudard reaction (2CO⇔CO₂+C) is also reduced by the gas-solid reaction of carbon monoxide (produced from steam reforming) with the lattice oxygen (CO+O_x⇔CO₂+O_x−1).     

Mechanical and dielectric properties of short carbon fiber reinforced Al2O3 composites with MgO additive

A series of short-carbon-fiber/Al₂O₃ composites with MgO as sintering additive were fabricated by pressureless sintering process. The effects of short carbon fiber (C_sf) content on the mechanical, dielectric and microwave absorbing properties of the composite were investigated. The results show that the addition of MgO enhances the density, hardness and the flexural strength of the alumina ceramic. However, these mechanical properties of the C_sf/Al₂O₃–MgO composite decrease with increasing C_sf content. Both the real and imaginary parts of the complex permittivity increase with increasing C_sf content in the frequency range of 8.2–12.4 GHz, which is attributed to the increasing electron polarization and associated polarization relaxation, respectively. When the C_sf content is 0.3 wt%, the reflection loss less than −10 dB and the minimum value of −27 dB are obtained with the coating thickness being 1.4 mm. The results indicate that the C_sf/Al₂O₃ with MgO is an excellent candidate for microwave absorbing material with favorable mechanical property.     

Steam reforming of LPG over Ni and Rh supported on Gd-CeO2 and Al2O3: Effect of support and feed composition

The steam reforming of liquefied petroleum gas (LPG) over Ni- and Rh-based catalysts supported on Gd-CeO₂ (CGO) and Al₂O₃ was studied at 750-900 °C. The order of activity was found to be Rh/CGO > Ni/CGO ∼ Rh/Al₂O₃ > Ni/Al₂O₃; we indicated that the comparable activity of Ni/CGO to precious metal Rh/Al₂O₃ is due to the occurring of gas-solid reactions between hydrocarbons and lattice oxygen () on CGO surface along with the reaction taking place on the active site of Ni, which helps preventing the carbon deposition and promoting the steam reforming of LPG.The effects of O₂ (as oxidative steam reforming) and H₂ adding were further studied over Ni/CGO and Ni/Al₂O₃. It was found that the additional of these compounds significantly reduced the amount of carbon deposition and promoted the conversion of hydrocarbons (i.e., LPG as well as CH₄, C₂H₄ and C₂H₆ occurred from the thermal decomposition of LPG) to CO and H₂. Nevertheless, the addition of too high O₂ oppositely decreased H₂ yield due to the oxidizing of Ni particle and the possible combusting of H₂ generated from the reaction, while the addition of too high H₂ also negatively affect the catalyst activity due to the occurring of catalyst active site competition and the inhibition of gas-solid reactions between the gaseous hydrocarbon compounds and on the surface of CGO (for the case of Ni/CGO).     

Hydrogen production via gasification of meat and bone meal in two-stage fixed bed reactor system

Gasification of meat and bone meal followed by thermal cracking of tar was carried out at atmospheric pressure using a two-stage fixed bed reaction system in series. The first stage was used for the gasification and the second stage was used for thermal cracking of tar. In this work, the effects of temperature (650-850 °C) of both stages, equivalence ratio (actual O₂ supply/stoichiometric O₂ required for complete combustion) (0.15-0.3) and the second stage packed bed height (40-100 mm) on the product (char, tar and gas) yield and gas (H₂, CO, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈) composition were studied. It was observed that the two-stage process increased hydrogen production from 7.3 to 22.3 vol.% (N₂ free basis) and gas yield from 30.8 to 54.6 wt.% compared to single stage. Temperature and equivalence ratio had significant effects on the hydrogen production and product distribution. It was observed that higher gasification (850 °C) and cracking (850 °C) reaction temperatures were favorable for higher gas yield of 52.2 wt.% at packed bed height of 60 mm and equivalence ratio of 0.2. The residence time of tar and product gases was varied by varying the packed bed height of second stage. The tar yield decreased from 18.6 wt.% to 14.2 wt.% and that of gas increased from 50.6 wt.% to 54.6 wt.% by changing the packed bed height of second stage from 40 to 100 mm while the gross heating value (GHV) of the product gas remained almost constant (16.2-16.5 MJ/m³).     

The controllable microstructure of porous Al2O3 ceramics prepared via a novel freeze casting route

In traditional aqueous slurry freezing casting processing, the growth method of ice crystals is hard to control, resulting in the uncontrollable pore's morphologies of the porous ceramics. In the experimental, the pure Al₂O₃ sol was used to substitute water as a medium for preparing ceramic slurry. With Al₂O₃ sol addition, it becomes easy to control the microstructure and pore's morphologies of the porous Al₂O₃ ceramics via adjusting of the solid loading, composition of the ceramic slurries, as well as the cooling methods. The SEM micrographs showed that the sol-contained ceramic slurry combined with freeze casting processing can easily prepare the porous Al₂O₃ ceramics with different pore sizes and different morphologies. The porous Al₂O₃ ceramics prepared from 70 wt.% to 90 wt.% solid loading sol-contained Al₂O₃ slurries and sintered at 1500 °C for 2 h have open porosities from 81.7% to 64.6%.     

Carbon nanotube/boehmite-derived alumina ceramics obtained by hydrothermal synthesis and spark plasma sintering (SPS)

Preparation, structure and properties of hydrothermally treated carbon nanotube/boehmite (CNT/γ-AlOOH) and densification with spark plasma sintering of Al₂O₃ and CNT/Al₂O₃ nanocomposites were investigated. Hydrothermal synthesis was employed to produce CNT/boehmite from an aluminum acetate (Al(OH)(C₂H₃O₂)₂) and multiwall-CNTs mixture (200 °C/2 h.). TEM observations revealed that the size of the cubic shape boehmite particles lies around 40 nm and the presence of the interaction between surface functionalized CNTs and boehmite particles acts to form ‘nanocomposite particles’. Al₂O₃ and CNT/Al₂O₃ compact bodies were formed by means of spark plasma sintering (SPS) at 1600 °C for 5 min using an applied pressure of 50MPa resulting in the formation of stable α-Al₂O₃ phase and CNT–alumina compacts with nearly full density. It was also found that CNTs tend to locate along the alumina grain boundaries and therefore inhibit the grain coarsening and cause inter-granular fracture mode. The DC conductivity measurements reveal that the DC conductivity of CNT/Al₂O₃ is 10^?4 S/m which indicate that there is a 4 orders of magnitude increase in conductivity compared to monolithic Al₂O₃. The results of the microhardness tests indicate a slight increase in hardness for CNT/Al₂O₃ (28.35 GPa for Al₂O₃ and 28.57 GPa for CNT/Al₂O₃).     

Direct synthesis of hydrogen peroxide from hydrogen and oxygen over a Pd core-silica shell catalyst

Pd core–silica shell particles (Pd@SiO₂) were prepared by encapsulating Pd colloids with a silica shell through the Stöber method. The palladium core particles were well dispersed (Dispersion = 43%) and had uniform size (4 nm) and shape inside the porous silica shell. Pd@SiO₂ showed good catalytic activity (554 mmol H₂O₂/g Pd·h) for the direct synthesis of H₂O₂, which was better than those of impregnated Pd catalysts (Pd/SiO₂ and Pd/Al₂O₃). It is expected that the stabilization of less coordinated Pd crystals in a highly dispersed state by core-shell formation is effective for the improvement of H₂O₂ production.     

Nanocrystalline In2O3-SnO2 thick films for low-temperature hydrogen sulfide detection

Nanocrystalline In₂O₃-SnO₂ thick films were fabricated using the screen-printing technique and their responses toward low concentrations of H₂S in air (2-150 ppm) were tested at 28-150 °C. The amount of In₂O₃-loading was varied from 0 to 9 wt.% of SnO₂ and superb sensing performance was observed for the sensor loaded with 7 wt.% In₂O₃, which might be attributed to the decreased crystallite size as well as porous microstructure caused by the addition of In₂O₃ to SnO₂ without structural modification. The interfacial barriers between In₂O₃ and SnO₂ might be another major factor. Typically, the response of 7 wt.% In₂O₃-loaded SnO₂ sensor toward 100 ppm of H₂S was 1481 at room temperature and 1921 at optimal operating temperature (40 °C) respectively, and showed fast and recoverable response with good reproducibility when operated at 70 °C, which are highly attractive for the practical application in low-temperature H₂S detection.     

Deposition behavior and characteristics of hydroxyapatite coatings on Al2O3, Ti,and Ti6Al4V formed by a chemical bath method

A simple chemical bath method was used to deposit hydroxyapatite (HA) coatings on Al₂O₃, Ti, and Ti6Al4V substrates at ambient pressure by heating to 65–95 °C in an aqueous solution prepared with Ca(NO₃)₂·4H₂O, KH₂PO₄, KOH, and EDTA. The deposition behavior, morphology, thickness, and phase of the coatings were investigated using scanning electron microscopy and X-ray diffractometry. The bonding strength of the coatings was measured using an epoxy resin method. The HA coatings deposited on the three kinds of substrates were fairly dense and uniform and exhibited good crystallinity without any additional heat treatment. A coating thickness of 1–1.8 μm was obtained for the samples coated once. By repeating the coating process three times, the thickness could be increased to 4.5 μm on the Al₂O₃ substrate. The bonding strength of these coatings was 18 MPa.     

Kinetics of the carbothermal synthesis of Mo carbide catalyst supported on various semiconductor oxides

Molybdenum carbide synthesized by temperature-programmed carburization of MoO₃ supported on various semiconductor oxides (10 wt.% Mo) with a H₂/C₃H₈ mixture have been characterized and evaluated for Fischer-Tropsch synthesis. The carburization reaction appeared to be a 2-stage process involving formation of intermediate oxycarbide phase, which was further carburized to the metal carbide form. Both α-MoC_1 − x and β-MoC_1 − x phases were detected in all Mo carbide catalysts and MoO₃ was converted completely to molybdenum carbide during carburization. The carburization rate depended on the C₃H₈ composition in the feed and attained an optimum at a H₂:C₃H₈ ratio = 5 for all four supports (Al₂O₃, TiO₂, SiO₂, and ZrO₂). Carbide formation rate increased with Mo loading although it reached a ‘plateau’ at Mo loading beyond 15 wt.% Mo. The existence of a compensation effect and isokinetic relationship for both oxycarbide and carbide phases suggested that the conversion of Mo oxide to oxycarbide and oxycarbide to carbide phase was governed by the same topotactic mechanism. Mo carbide catalysts were evaluated for CO hydrogenation activity and Fischer-Tropsch specific reaction rate decreased in the order; MoC_1 − x/TiO₂ > MoC_1 − x/SiO₂ > MoC_1 − x/ZrO₂ > MoC_1 − x/Al₂O₃ parallel to the trend for Mo carbide production rate.     

Catalytic conversion of C12–C14 primary alcohols mixture into long-chain ketones

A charge of raw primary alcohols of high molecular weight from commercial plant was transformed into long-chain ketones fraction of potential commercial use. In this continuous flow method LaMnO₃/La–Al₂O₃ catalyst was used. At 420 °C and a normal pressure mixture of 74.2 wt.% C₁₂ and 25.8 wt.% C₁₄ primary alcohols and toluene (weight ratio alcohols:toluene = 1:1) was converted into ketones with 73.4% yield in relation to the theoretical value. Ketones were analyzed by TLC, NMR and GC-MSD.     

Hydroisomerization-cracking of gasoline distillate from Fischer-Tropsch synthesis over bifunctional catalysts containing Pt and heteropolyacids

A gasoline distillate from the Fischer-Tropsch synthesis (so-called as F-T gasoline) was collected in a cold trap set in a gas-flowed slurry reaction system. The F-T gasoline contained 92.8 wt.% n-alkanes (ranged from n-C₄H₁₀ to n-C₁₄H₃₀), 2.4 wt.% 1-alkenes, and 4.8 wt.% iso-alkanes. By the hydroisomerization-cracking in an atmospheric flowed fixed-bed reactor over the catalysts containing Pt and heteropoly compound Cs_2.5H_0.5PW₁₂O₄₀ (abbreviated as Cs2.5), the F-T gasoline was converted to gasoline distillated mixed alkanes with a high iso/n ratio. A mechanical mixture of Pt/Al₂O₃ and Cs2.5 (noted as Pt/Al₂O₃ + Cs2.5) showed the highest catalytic performance among various catalysts. The product over Pt/Al₂O₃ + Cs2.5 after 5 h on-steam at 523 K contained 94.4% C₅-C₉ (gasoline components) with a high iso/n ratio of 8.45. The co-grinding time of Pt/Al₂O₃ and Cs2.5 influenced the catalytic performance when the time was shorter than 10 min but gave little influence on the catalytic performance when the time was longer than 10 min. Because the iso/n ratio of products over Pt/Al₂O₃ + Cs2.5 increased by adding Pt in Cs2.5 and decreased with increasing H₂/feedstock, the reaction proceeded through a bifunctional mechanism in which Pt sites achieved a hydrogenation/dehydrogenation function and acid sites achieved an isomerization/cracking function. The balance of Pt and solid acids was important to obtain a high catalytic performance in the hydroisomerization-cracking of F-T gasoline. Because Cs2.5 possessed moderate acidic strength and uniformly distributed acidic sites, Pt/Al₂O₃ + Cs2.5 showed a higher catalytic stability than that over Pt/Al₂O₃ + SO₄/ZO₂ and showed a higher catalytic activity than that over Pt/Al₂O₃ + H-ZSM-5.     

Effect of magnesium addition on catalytic performance of PtSnK/γ-Al2O3 catalyst for isobutane dehydrogenation

The effect of magnesium addition on the catalytic properties of PtSnK/γ-Al₂O₃ catalyst for isobutane dehydrogenation has been investigated by reaction tests and some physicochemical characterizations such as nitrogen adsorption, TEM, H₂ chemisorption, TPR, H₂-TPD, and TPO. It was found that with the suitable addition of magnesium (0.2 and 0.4 wt.%), the platinum dispersion increased, while the carbon depositions decreased. The presence of Mg in the PtSnMgK/γ-Al₂O₃ catalysts could not only strengthen the Sn-Al₂O₃ interaction, but also stabilize the oxidation states of Sn species, which resulted in the increased reaction activity and stability. However, when the content of magnesium was excessive (0.6 and 0.8 wt.%), the character of platinum and the interfacial properties between the metal and the support changed evidently, which was disadvantageous to the reaction. In our experiments, addition of 0.4 wt.% Mg to PtSnK/Al₂O₃ catalyst showed the best catalytic performance. After reaction for 6 h, selectivity toward isobutene of higher than 94% was achieved with the corresponding conversion value of about 29.0%.     

Enhanced propylene/propane separation by carbonaceous membrane derived from poly (aryl ether ketone)/2,6-bis(4-azidobenzylidene)-4-methyl-cyclohexanone interpenetrating network

An innovative combination of a photosensitive crosslinker, 2,6-bis(4-azidobenzylidene)-4-methyl-cyclohexanone (Azide) with poly (aryl ether ketone) (PAEK) is utilized to form a semi-interpenetrating network (IPN) as the precursor for carbon membranes. Low temperature pyrolysis (450-650 °C) of this precursor produces carbon membranes with excellent olefin/paraffin separation performance that surpasses the conventional trade-off line. The carbon membranes have reasonably good flexibility since excessive closure of the micropores is avoided. This is evident from the mechanical properties of the carbon membranes obtained from nanoindention to the pore size distribution derived from CO₂ adsorption. By varying the composition of Azide/PAEK and optimizing the low-temperature pyrolysis protocol, it was found that PAEK/Azide (80:20) pyrolysed at 550 °C exhibits the best propane/propylene separation performance with C₃H₆ permeability of 48 barrer and ideal C₃H₆/C₃H₈ selectivity of 44. Due to strong competitive sorption of propane and propylene molecules, the C₃H₆ permeability is lowered to 3.6 barrer and the C₃H₆/C₃H₈ selectivity to 32 in mixed gas experiments. However, this separation performance is still above the trade-off line. Even though both Azide and PAEK cannot form useful carbon membranes, their IPN is a unique precursor that can produce carbon membranes with comparable performance.     

Raising Co/Al2O3 catalyst lifetime in Fischer–Tropsch synthesis by using a novel dual-bed reactor

Accelerated deactivation of 15 wt.% Co/Al₂O₃ catalyst in Fischer–Tropsch synthesis (FTS) in a single-bed and a dual-bed reactor is reported. Water was found to have a remarkable effect on the deactivation of Co/Al₂O₃ catalyst during FTS. Synthesis at higher temperatures and lower space velocities resulted in higher values of P_H2O/(P_CO + P_H2) and P_H2O/P_CO and higher catalyst deactivation rates. Water-induced back-oxidation of cobalt, cobalt–alumina interactions, irreducible cobalt aluminates formation and refractory coke formation are the main sources of deactivation. When the water to carbon monoxide plus hydrogen ratio P_H2O/(P_CO + P_H2) is greater than about 0.55 or water to carbon monoxide ratio P_H2O/P_CO is greater than about 1.5, it is not uncommon to find rapid catalyst deactivation. Separation of water and heavy hydrocarbons between the two catalytic beds of the dual-bed reactor, resulted in 62% lower catalyst deactivation rate than that of the single-bed reactor. The amount of refractory coke formation on the catalysts of the dual-bed reactor is 34% lower than that of the single-bed reactor. It was revealed that activity recovery of the used catalysts of the dual-bed is higher than that of the single-bed reactor.