Hydro-conversion of 1-methyl naphthalene into (alkyl)benzenes over alumina-coated USY zeolite-supported NiMoS catalysts

Hydro-conversion reactions were carried out at 360 °C under 5 MPa of H₂ pressure to study ring opening reactions of 1-methyl naphthalene using NiMoS supported on γ-alumina and alumina-coated/mixed USY zeolites. The catalysts were characterized using N₂ BET, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), pyridine FT-IR, and high-resolution transmission electron microscopy (HR-TEM) to study the influence of morphological and acidic properties on hydrogenation (HYD) and hydrocracking (HC) reactions. NMACZ-2 (NiMoS supported on the minimum amount of alumina-coated USY zeolite) showed enhanced reactivity for HC and produced (alkyl)benzenes with the highest yield, of ca. 80%. By-products were tetralin, decalin and cyclo-paraffin species. The tetralin species produced using NMACZ-2 moved into the alumina-coated USY zeolite support before undergoing HYD to produce decalin species, which were rapidly and selectively hydro-cracked into (alkyl)benzenes. A large amount of decalin was produced through the HYD of tetralin without significant cracking, possibly due to the weak acid character of γ-alumina. Bulk phase Mo oxide species on NMAZ (physical mixture of alumina and USY zeolite), as well as deactivation of the catalysts due to coke formation over the naked zeolite surface, inhibited the ring opening of tetralin, decreasing the yield of (alkyl)benzene. Various morphologies, such as the MoS₂ structure and acidic characteristics of the catalysts, were crucial factors affecting the HC reactivity of 1-methyl naphthalene.     

Analysis and removal of heteroatom containing species in coal liquid distillate over NiMo catalysts

Heteroatom containing molecules in South Banko coal liquid (SBCL) distillate were identified with a gas chromatograph equipped with an atomic emission detector (GC-AED). Thiophenes and benzothiophenes were found to be the major sulfur compounds. Pyridines, anilines, and phenols were the major nitrogen and oxygen compounds, respectively. Reactivities of heteroatom containing species in hydrotreatment over conventional NiMoS/Al₂O₃, NiMoS/Al₂O₃–SiO₂ catalysts were very different according to their cyclic structure as well as the kind of heteroatom in the species. The sulfur species were completely desulfurized over the catalysts examined in the present study by 60 min at 360 °C under initial hydrogen pressure of 5 MPa. However, hydrodenitrogenation was more difficult than hydrodesulfurization even at 450 °C. Anilines were found the most refractory ones among the nitrogen species. Hydrodeoxygenation of SBCL was also difficult in the hydrotreatment conditions examined in the present study. Dibenzofuran was the most refractory molecule among the oxygen species. A two-stage reaction configuration at 340 and 360 °C improved HDN and HDO reactivities, although the conversions were still insufficient. Increasing the acidity of the support as well as the loading of the metals on the NiMoS/Al₂O₃ catalysts improved very much the heteroatom reduction to achieve complete removal of nitrogen by two-stage reaction configuration at 340–360 °C and oxygen at 360 °C, respectively. The addition of H₂S in the reaction atmosphere inhibited the HDN reaction but increased markedly the HDO conversion. The acidic support increased the activity in hydrotreatment through enhancing the hydrogenation activity, while H₂S maintained the catalyst in a sufficiently sulfided state.     

Processing and properties of sol gel derived alumina–carbon nano tube composites

High purity alumina–carbon nano tube (CNT) composites were prepared by an aqueous sol–gel processing route. CNTs were dispersed in alumina sol containing appropriate amount of MgO precursor. Aqueous slurry of alumina was seeded into the sol followed by gelation, drying and calcination at 1000 °C for 1 h. The calcined powder consisting of alumina-coated CNTs and alumina was milled, sieved, dried, pressed and pressureless sintered at 1400–1600 °C for 1 h in nitrogen atmosphere. Sintered samples were further isostatically hot pressed at 1300 °C and the properties were compared with the pressureless sintered samples. Phase formation was followed by XRD study, CNT retention was confirmed by Raman studies and the samples were further characterized for mechanical and microstructural properties.     

Preparation processes and characterizations of alumina-coated alumina support layers and alumina-coated natural material-based support layers for microfiltration

Recently, porous ceramic membranes have become a subject of significant interest due to their outstanding thermal and chemical stability. To reduce the high manufacturing costs of these porous ceramic membranes, recent research has focused on the utilization of inexpensive natural materials. However, there have not been any well-established direct comparisons of the membrane properties between typical alumina-based membranes and novel natural material-based membranes. Therefore, we compared alumina-coated alumina support layers (with average pore sizes ranging from 0.10 µm ~0.18 µm), alumina-coated diatomite-kaolin composite support layers (with an average pore size of 0.12 µm), and alumina-coated pyrophyllite-diatomite composite support layers (with an average pore size of 0.11 µm) via the dip-coating method and subsequent heat treatment ranging from 1200 °C–1400 °C for 1 h. The pure water permeability of the alumina-coated diatomite-kaolin composite support layer and the alumina-coated pyrophyllite-diatomite composite support layer was found to be approximately 2.0×10² L m⁻² h⁻¹ bar⁻¹, which is similar to that of an alumina-coated alumina support layer. Therefore, we suggest that the average pore size of an alumina-coated natural material-based support layer can be effectively controlled while exhibiting acceptable water permeability.     

Formation of multi-walled carbon nanotubes by Ni-catalyzed decomposition of methane at 600–750 °C

Ni-catalyzed decomposition of methane at high temperatures was examined by using a thermogravimetric apparatus. The catalyst (10 wt.% Ni supported on spherical alumina) gave quite a high carbon nanotube (CNT) yield at the temperatures below 680 °C. At > 700 °C, however, carbon formation rate decreased with increasing the reaction temperature. Temperature-programmed reaction also showed the maximum CNT growth rate at ~ 690 °C. This result ruled out the possibility that the apparent negative activation energy is caused by sintering of Ni particles. Detailed examination on the kinetic expression led us to a conclusion that the dissolution of carbon atoms formed by dissociation of methane into bulk of the nickel particles is the rate-determining step at high temperatures, while methane adsorption is the rate-determining step at lower temperatures. This idea also explains the fact that the carbon yield drastically decreased at high temperatures. The CNTs formed at these temperatures had thinner walls than those formed at lower temperatures. The latter fact also supports the idea that the solubility of carbon in the nickel particles decreases at high temperatures.     

A and X-type zeolites synthesised from kaolinite at low temperature

A commercial Chinese well crystalline kaolinite (KCh) and a poorly crystalline kaolinite (KGa-2) from the Source Clay Repository of The Clay Minerals Society were used, after fusion with NaOH, to synthesise zeolite by hydrothermal activation. The experiments were performed at temperatures ranging from 25 to 60 °C, for 96 h, in distilled water. A large amount of X-type zeolite was crystallised from KCh at 25 °C whereas its crystallisation from KGa-2 starts at 35 °C. A-type zeolite is formed using both source materials and it is the only synthetic product detected at 25 °C. The presence of illite/mica and quartz in KCh determines the different behaviour of the two starting clay minerals.     

Synthesis and characterization of Li-type EDI zeolite

A Li-type EDI zeolite (Li-EDI) was successfully synthesized in the Li₂O–Al₂O₃–SiO₂–H₂O system using a silica–alumina mixed sol as the starting material in the absence of other chemical species. The characterization of the obtained Li-EDI was compared with that of the Li-exchanged Linde F zeolite (K-type EDI zeolite). Starting gels with the batch composition of xLi₂O·Al₂O₃·2SiO₂·275H₂O (x = 2–5) were prepared by adding a LiOH solution to a silica–alumina mixed sol. A hydrothermal reaction of the gels was carried out at various temperatures. Li-EDI formed from all of the batches in the range of 60–100 °C. However, the ABW-type zeolite co-crystallized in the composition of Li₂O/Al₂O₃ of 2.0–3.0 above 90 °C. The crystal morphology of Li-EDI was a prism shape. The average particle size of Li-EDI is 0.69 μm in length and 0.23 μm in width. The crystal structure of the Li-EDI collapsed at 300 °C, which indicated that the thermal stability of Li-EDI is significantly lower than that of the Linde F zeolite, which is stable up to 1000 °C.     

Modeling thermal and catalytic conversion of decalin under industrial FCC operating conditions

The processability of decalin, a two-fused ring cycloparaffin, in the absence and presence of USY catalysts of different zeolite crystallite sizes is investigated under actual FCC conditions. Thermal and catalytic cracking experiments using decalin are carried out in the mini-fluidized CREC riser simulator. This novel unit operates under relevant FCC process conditions in terms of partial pressures of decalin, temperatures (450–550 °C), contact times (3–7 s), catalyst–decalin mass ratios (5) and using well-fluidized catalysts. Decalin overall conversions ranged between 8–19wt% at low reaction temperatures and 14–27 wt% at high temperatures. It is found that decalin undergoes reactions such as ring opening, protolytic cracking, isomerization, hydrogen transfer and transalkylation. A heterogeneous kinetic model for decalin conversion including thermal effects, adsorption and intrinsic catalytic reaction phenomena is established. Adsorption and kinetic parameters are determined, including the heat of adsorption (?61 kJ/mol) as well as thermal and primary catalytic intrinsic activation energies, which are in the range of 56–59 kJ/mol and 74–91 kJ/mol, respectively. It is determined that hydrogen transfer reactions are more pronounced and selectively favored against other reactions at lower reaction temperatures, while ring-opening and cracking reactions predominate at higher reaction temperatures.     

Oxidation protection of carbon fibers by coating with alumina and/or titania using atomic layer deposition

Alumina and titania coatings were deposited by atomic layer deposition onto carbon fibers at temperatures of 200 °C or below and reduced pressure. The coatings were smooth, uniform and conformed to the fiber surface. Thermogravimetric analysis (TGA) revealed that the coatings improved the oxidation resistance of the carbon fibers: the oxidation onset temperature of uncoated fibers and fibers coated with 66 nm of alumina was 630 °C. For fibers coated with 20 nm of titania it was 550 °C. Double layer coatings by 50 nm of alumina followed by 13 nm of titania yielded an oxidation onset temperature of 660 °C, while changing the order of the layers, i.e., coating fibers first with 20 nm of titania followed by 30 nm of alumina yielded an oxidation onset temperature of 750 °C. These TGA results were confirmed by a set of additional oxidation experiments conducted at a fixed temperature of 550 °C using a tube furnace in air. In this latter set of additional experiments, the times needed for a complete oxidation of the above mentioned samples were 8 h, 12 h, 10 h, 13 h, and 30 h, respectively.     

Characterization of high strength mortars with nano alumina at elevated temperatures

In this study, the effect of elevated temperatures on chemical composition, microstructure and mechanical properties of high strength mortars with nano alumina was investigated. Mortars with 1, 2 and 3% nano alumina as cement replacement were prepared and then exposed to 100 °C, 200 °C, 300 °C, 400 °C, 600 °C, 800 °C and 1000 °C. XRD, DSC and SEM tests were carried out to identify chemical composition and microstructure changes in the cement matrix after being exposed to elevated temperatures. Residual compressive strength, relative elastic modulus and gas permeability coefficient of samples were also obtained. A brittleness index was defined to monitor changes in brittleness of samples after being exposed to elevated temperatures. Nano alumina enhanced compressive strength of samples up to 16% and improved residual compressive strength. An increase in the relative elastic modulus, higher energy absorption and lower permeability were also observed when 1% nano alumina was added.     

A kinetic study of gaseous potassium capture by coal minerals in a high temperature fixed-bed reactor

The reactions between gaseous potassium chloride and coal minerals were investigated in a lab-scale high temperature fixed-bed reactor using single sorbent pellets. The applied coal minerals included kaolin, mullite, silica, alumina, bituminous coal ash, and lignite coal ash that were formed into long cylindrical pellets. Kaolin and bituminous coal ash that both have significant amounts of Si and Al show superior potassium capture characteristics. Experimental results show that capture of potassium by kaolin is independent of the gas oxygen content. Kaolin releases water and forms metakaolin when heated at temperatures above 450 °C. The amounts of potassium captured by metakaolin pellet decreases with increasing reaction temperature in the range of 900–1300 °C and increases again with further increasing the temperature up to 1500 °C. There is no reaction of pre-made mullite with KCl at temperatures below 1300 °C. However, the weight gain by mullite is only slightly smaller than that by kaolin in the temperature range of 1300–1500 °C. A simple model was developed for the gas–solid reaction between potassium vapor and metakaolin pellet at 900 °C.     

Type-A zeolites with hydroxyapatite surface layers formed by an ion exchange reaction

To enhance adsorption of harmful ions on type-A zeolites (LTA), hydroxyapatite (HAp) thin layers were synthesized on the LTA surface by an ion exchange reaction of Ca²⁺ for NH₄⁺ under hydrothermal treatment. The temperatures and durations in the reactions were varied ranging from 25 to 200 °C and from 1 to 168 h. The samples synthesized were characterized by X-ray diffraction method (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmet–Teller method (BET). The structure of LTA was not destroyed by the hydrothermal treatments at 25 to 160 °C for 8 h and also at 120 °C for 1 to 72 h. The yield of HAp grown on the LTA surface, synthesized at 120 °C for 8 h, showed a maximum value of 0.82. The morphologies of HAp were dependent mainly on the temperatures. The specific surface area remained unchanged in the treatments at 25 to 40 °C for 8 h, as compared to the specific surface area of Ca-LTA, however up to 80 °C, the value decreased with an increase of exchange temperature.     

Reliable high strength alumina fabricated by DCC-HVCI using submicron calcium citrate complex

Ceramics with high strength and reliability are highly demanded in engineering applications. In this paper, a modified direct coagulation casting via high valence counter ions (DCC-HVCI) method for alumina using calcium citrate complex assisted by glycerol diacetate was investigated. Calcium citrate complex suspensions were prepared by mixing tri-ammonium citrate and calcium chloride in water. Effect of reaction time on the chelating properties of the prepared suspensions was investigated. Concentrated alumina suspensions with a solid loading of 50 vol% were prepared by mixing the calcium citrate complex suspensions and alumina powder at pH of 10.5. Then the suspensions were coagulated by adding 3–6 vol% glycerol diacetate at temperatures of 40–70 °C for 2–6 h. The compressive strength of the coagulated wet samples is in the range 1.1–2.4 MPa. Alumina ceramics sintered at 1550 °C shows homogeneous microstructures with flexural strength and Weibull modulus of 455±17 MPa and 30, respectively.     

Reducing sintering temperature of yttria stabilized zirconia through addition of lithium nitrate and alumina

Reducing sintering temperature of yttria stabilized zirconia (YSZ) has been achieved through doping with alumina and lithium nitrate at levels below 1 mol%. Sintering experiments of pure and doped samples have been conducted with the same profile using an optical dilatometer. All samples exhibited anisotropic sintering over a wide range of temperatures but final shrinkage values were comparable in axial and radial directions. Sintering temperature has been reduced by as much as 110 °C. We believe that the reduction in sintering temperatures is due to viscous flow in the first stage sintering. Bimetallic doping (mixture of alumina and lithium nitrate doping) is more effective in reducing sintering temperature than single doping possibly due to better distribution of doping material throughout the matrix material. Separate sintering experiments for 5 h have been conducted at 1250 °C and 1170 °C on doped 8 mol% and 3 mol% YSZ, respectively, and have shown that near full density (～96%) is reachable.     

Temperature induced gelation of non–aqueous alumina suspension using oleic acid as dispersant

A novel temperature induced gelation method for alumina suspension using oleic acid as dispersant is reported. Non–aqueous suspension with high solid loading and low viscosity is prepared using normal octane as solvent. Influence of oleic acid on the dispersion of suspension was investigated. There was a well disperse alumina suspension with 1.3 wt% oleic acid. Influence of gelation temperature on the coagulation process and properties of green body was investigated. The sufficiently high viscosity to coagulate the suspension was achieved at −20 °C. The gelation temperature was controlled between the melting point of dispersant and solvent. The gelation mechanism is proposed that alumina suspension is destabilized by dispersant separating out from the solvent and removing from the alumina particles surface. The alumina green body with wet compressive strength of 1.07 MPa can be demolded without deformation by treating 53 vol% alumina suspension at −20 °C for 12 h. After being sintered at 1550 °C for 3 h, dense alumina ceramics with relative density of 98.62% and flexural strength of 371±25 MPa have been obtained by this method.     

The resistance to oxidation of an HfB2–SiC composite

The oxidation resistance of an hot-pressed HfB₂–SiC composite was studied through non-isothermal and isothermal treatments at temperatures up to 1600 °C in air. The most severe oxidation conditions consisted of repeated heating-cooling cycles at 1600 °C for up to 80 min of exposure. A thermogravimetric test for over 20 h at 1450 °C provided evidence that, at this temperature, the oxidation kinetics fits a paralinear law until 10 h, when a partial rupture of external oxide scale occurs (i.e. a break-away reaction). Afterwards, the weight gain data fit a linear law. The main secondary phases formed in the composite during hot-pressing, namely BN, Hf(C,N) and a Si-based compound, although in limited amounts, influenced the oxidation resistance at temperatures below 1350 °C. At temperatures higher than about 1400 °C, the presence of SiC particles markedly improved the oxidation resistance due to the formation of a protective borosilicate glassy coating on the exposed surfaces.     

Low-temperature sintering of coarse alumina powder compact with sufficient mechanical strength

Coarse alumina powder compacts doped with various amounts of titania and copper oxide were pressurelessly sintered from 900 °C to 1600 °C. Their phase assemblages and microstructural evolution, as well as their properties, were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry/thermogravimetric (DSC/TG) analysis, and three-point bending and wetting test. The role of TiO₂ and CuO during the sintering is discussed in detail. The experimental results show that the liquid phase from the copper oxide appeared at approximately 1200 °C, so the solid-state reaction between alumina and titania took place at a lower temperature. Such solid state-reaction sintering had a strong impact on the grain growth and greatly promoted the densification of the alumina compact. In addition, the liquid phase inhibited the abnormal grain growth and microcracking. As a result, the coarse alumina powder compacts doped with 5 wt% TiO₂–CuO were fully densified and exhibited sufficient flexural strength (342±21 MPa) when sintered at a temperature of 1450 °C for 2 h.     

Improvement on characteristics of porous alumina from platelets using a TEOS treatment

A porous alumina body was synthesized from anisotropic alumina particles, namely platelets. When green compacts, which had been uniaxially pressed at 1 MPa, were heated at 1200 and 1500 °C for 1 h, the average porosity of the resulting alumina bodies was 75.5 and 71.0%, respectively. The thermal conductivity of the porous alumina fabricated at 1400 °C for 1 h with 72.3% in porosity was 0.8 W m^?1 K^?1. In an attempt to increase the compressive strength of the porous alumina bodies, TEOS (tetraethyl orthosilicate) solution treatment was carried out, followed by reheating to 1400 °C for 1 h. The compressive strength of the porous alumina body increased from 3.8 MPa (without TEOS solution treatment) to 10.2 MPa (with three rounds of TEOS treatment), with the porosity decreasing to 65.5% and the thermal conductivity increasing to1.2 W m^?1 K^?1.     

Suppression of grain growth in sub-micrometer alumina via two-step sintering method

Two-step sintering (TSS) was applied to suppress the accelerated grain growth of sub-micron (～150 nm) alumina powder. The application of an optimum TSS regime led to a remarkable decrease of grain size down to ～500 nm; while the grain size of the full-dense structures produced by conventional sintering ranged between 1 and 2 μm. To find how important the temperatures at sintering steps might be, several TSS regimes were conducted. The results showed that the temperatures at both sintering steps play vital roles in densification and grain growth of the alumina compacts. Based on the results, the optimum regime consisted of heating the green bodies up to 1250 °C (first step) and then holding at 1150 °C for more than 60 h (second step). This yielded the finest microstructure with no deterioration of the densification. Heating at 1300 °C (first step) and then at 1200 °C (second step) was not a successful procedure. Lowering the temperature of the second step down to 1100 °C resulted in exhaustion of the densification at 88% -theoretical density. A nearly full-dense structure with an average grain size of 850 nm was obtained when the temperature of the second step was increased to 1150 °C. Empirical results show that not only the first step temperature has to be high enough to reach a structure containing unstable pores, but the second sintering temperature must also be high enough to activate the densification mechanism without grain growth. This means that a considerable densification at the first step does not imply enough second-step densification.     

Hydrogen production by aqueous-phase reforming of ethanol over nickel catalysts prepared from hydrotalcite precursors

Derived hydrotalcite catalysts, with different Ni loadings, were prepared and tested in aqueous-phase reforming of ethanol. Upon calcination of the hydrotalcite-like compounds, there was formation of MgO periclase-type phase, where both nickel and aluminum oxides are well dispersed. The mixed oxides showed only one reduction peak in temperature range of 900–1000 °C. The catalytic tests were carried out in a batch reactor with an aqueous solution of 1 wt.% ethanol at different temperatures (200, 230 and 250 °C). The derived hydrotalcite catalysts showed high activity, with 65% of ethanol conversion at 230 °C, high hydrogen selectivity and lower methane production than alumina supported nickel catalyst.