Characterization of Pd catalysts supported on USY zeolites with different SiO2/Al2O3 ratios for the hydrogenation of naphthalene in the presence of benzothiophene

A series of ultra-stable Y-type (USY) zeolites with different SiO₂/Al₂O₃ ratios in the range of 10–80 were used as supports for preparing Pd/USY at 2 wt% Pd loading. The FT-IR of hydroxyl groups of USY zeolites, the n-butylamine chemisorption and the temperature-programmed desorption were used in combination to characterize the zeolite acidity. TPR, H₂-TPD and chemisorption using H₂ were used to characterize the Pd reduction and dispersion. The hydrogenation of naphthalene was conducted at 200 °C in the presence of benzothiophene at different sulfur/metal ratios. The hydrogenation activity, selectivity, and the sulfur tolerance strongly depended on the SiO₂/Al₂O₃ ratio (thus the acidity) of the zeolites. The activity decreased with increasing SiO₂/Al₂O₃ in this range. The IR and n-butylamine TPD showed that both the amount and strength of Brönsted acidity decreased with the increase of the SiO₂/Al₂O₃ ratio. The good relationship between the acidity modification and catalytic performance suggests that the sulfur tolerance of Pd/USY zeolite might be due to the desired metal-support interaction, which resulted in larger amount of electron-deficient Pd. However, as shown in TGA and TPO-IR studies, the higher hydrogenation performance on more acidic zeolite also caused higher amount of carbonaceous species on the catalyst.     

The effect of sodium on the catalytic activity of ZnO–Al2O3/ZSM-5 and SnO–Al2O3/ZSM-5 for the transesterification of vegetable oil with methanol

In order to elucidate the effect of sodium on the activity of ZSM-5 supported metal oxides catalysts (ZnO–Al₂O₃/ZSM-5 and SnO–Al₂O₃/ZSM-5) for the transesterification of soybean oil with methanol, ZSM-5 supported metal oxides were prepared with and without sodium hydroxide by impregnation. The metal compositions of the ZSM-5 supported metal oxide catalysts and the metal concentrations dissolved from the catalysts to the methylester phase were measured by SEM-EDS and inductive coupled plasma spectroscopy, respectively. The catalytic activity of ZnO–Al₂O₃/ZSM-5 and SnO–Al₂O₃/ZSM-5 containing sodium did not originate from surface metal oxides sites, but from surface sodium sites or dissolved sodium leached from the catalyst surface.     

Properties and rapid consolidation of nanostructured Al2O3-Al2SiO5 composites by high frequency induction heated sintering

The rapid sintering of nanostructured Al₂O₃ and Al₂O₃ to Al₂SiO₅ composites was investigated by a high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Highly dense nanostructured Al₂O₃ and Al₂O₃ to Al₂SiO₅ composites were produced with simultaneous application of a 80 MPa pressure and induced output current of a total power capacity (15 kW) within 3 min. The sintering behavior, grain size and mechanical properties of Al₂O₃ and Al₂O₃ to Al₂SiO₅ composites were investigated.     

Adsorption of hydrocarbons by ZSM-5 zeolites with different SiO2/Al2O3 ratios: a combined FTIR and gravimetric study

In metal-free ZSM-5, the decrease in the concentration of Bronsted and Lewis acid sites parallels the increase in the SiO₂/Al₂O₃ ratio. In the presence of residual moisture, the adsorption of small alkanes does not markedly depend on the SiO₂/Al₂O₃ ratio in the range from 30 to 150. The acidity is more important for the adsorption of alkenes (propene) which oligomerize following adsorption. The addition of 5 wt.% of La does not significantly affect the strength of the surface acid sites but does decrease their concentration. It causes a transformation, in a part, of the Bronsted acid sites. These new centers could perhaps be assigned to LaO(OH) or La(OH)₂⁺ species which may be formed on the surface in La-containing ZSM-5. La could exchange only the strongest acidic sites without inducing large changes in their total concentration. La addition has a very small effect on the adsorption of small hydrocarbons. The exchange of the protons by Cu²⁺ decreases the concentration of Bronsted acid sites. At a sufficient loading of the ZSM-5 by Cu²⁺, i.e. at an atomic ratio Cu/Al > 1.0, the exchange can almost totally suppress the Bronsted acidity. Another effect of the ion exchange is the suppression of the adsorption capacity of small hydrocarbons due to lowered surface area and internal pore volume. The lowered available internal pore volume also limits the extent of the oligomerization of propene.     

Corrosion mechanisms of Al2O3/MgAl2O4 by V2O5, NiO, Fe2O3 and vanadium slag

The effects of V₂O₅, NiO, Fe₂O₃ and vanadium slag on the corrosion of Al₂O₃ and MgAl₂O₄ have been investigated. The specimens of Al₂O₃ and MgAl₂O₄ with the respective oxides above mentioned were heated at 10 °C/min from room temperature up to three different temperatures: 1400, 1450 and 1500 °C. The corrosion mechanisms of each system were followed by XRD and SEM analyses. The results obtained showed that Al₂O₃ was less affected by the studied oxides than MgAl₂O₄. Alumina was only attacked by NiO forming NiAl₂O₄ spinel, while the MgAl₂O₄ spinel was attacked by V₂O₅ forming MgV₂O₆. It was also observed that Fe₂O₃ and Mg, Ni, V and Fe present in the vanadium slag diffused into Al₂O₃. On the other hand, the Fe₂O₃ and Ca, S, Si, Na, Mg, V and Fe diffused into the MgAl₂O₄ structure. Finally, the results obtained were compared with those predicted by the FactSage software.     

Microstructure and mechanical properties of Al2O3/Er3Al5O12 eutectic rods grown by the laser-heated floating zone method

Eutectic rods of Al₂O₃-Er₃Al₅O₁₂ were grown by directional solidification using the laser-heated floating zone method at rates in the range 25-1500 mm/h. Their microstructure and mechanical properties (hardness, toughness and strength) were investigated as a function of the growth rate. A homogeneous and interpenetrated microstructure was found in most cases, and interphase spacing decreased with growth rate following the Hunt-Jackson law. Hardness increased slightly as the interphase spacing decreased while toughness was low and independent of the microstructure. The rods presented very high bending strength as a result of the homogeneous microstructure, and their strength increased rapidly as the interphase spacing decreased, reaching a maximum of 2.7 GPa for the rods grown at 750 mm/h. The bending strength remained constant up to 1300 K and decreased above this temperature. The relationship between the microstructure and the mechanical properties was established from the analysis of the microstructure and of the fracture mechanisms.     

Phase diagram of the Al2O3-HfO2-Y2O3 system

The phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system was first constructed in the temperature range 1200-2800 °C. The phase transformations in the system are completed in eutectic reactions. No ternary compounds or regions of appreciable solid solution were found in the components or binaries in this system. Four new ternary and three new quasibinary eutectics were found. The minimum melting temperature is 1755 °C and it corresponds to the ternary eutectic Al₂O₃ + HfO₂ + Y₃Al₅O₁₂. The solidus surface projection, the schematic of the alloy crystallization path and the vertical sections present the complete phase diagram of the Al₂O₃-HfO₂-Y₂O₃ system.     

Tribological properties of Al2O3 nanoparticles as lubricating oil additives

Nano-scale Al₂O₃ spherical particles, prepared via a hydrothermal method and modified by silane coupling agent, can be well-dispersed in lubricating oil. The tribology properties of Al₂O₃ nanoparticles as lubricating oil additives have been studied by four-ball and thrust-ring friction test, which illustrate that the modified Al₂O₃ nanoparticles can effectively improve the lubricating behaviors compared to the base oil. When the added concentration is 0.1 wt%, the friction coefficient and the wear scar diameter are both smallest. The lubrication mechanism is that a self-laminating protective film is formed on the friction surface and the wear behavior changes from sliding friction to rolling friction.     

Influence of CuO on the formation and coexistence of 3CaO·SiO2 and 3CaO·3Al2O3·CaSO4 minerals

The influence of CuO on the formation and coexistence of 3CaO·SiO₂ and 3CaO·3Al₂O₃·CaSO₄ minerals in Portland cement containing 3CaO·3Al₂O₃·CaSO₄ mineral is reported in this paper. The results show that a suitable amount of CuO can lower the clinkering temperature and improve the burn-ability of clinkers. It can also promote the formation of 3CaO·SiO₂ and 3CaO·3Al₂O₃·CaSO₄ minerals and facilitate the coexistence of the two minerals in the clinkers. But adding 1% CuO to the raw material can cause the decomposition of 3CaO·3Al₂O₃·CaSO₄.     

Steady State Isotopic Transient Kinetic Analysis of Flameless Methane Combustion over Pd/Al2O3 and Pt/Al2O3 Catalysts

The SSITKA measurements were performed in the steady state of complete methane oxidation on the Pd/Al₂O₃ and Pt/Al₂O₃ catalysts. It was found that the number of intermediates and their average life-time on the catalyst surface changes with the increase of reaction temperature. On the Pd/Al₂O₃ catalyst there is larger number of active centres than on Pt/Al₂O₃ catalyst which permits the course of methane oxidation at lower temperatures.     

A novel solid superbase of Eu2O3/Al2O3 and its catalytic performance for the transesterification of soybean oil to biodiesel

A novel solid superbase catalyst of Eu₂O₃/Al₂O₃ was prepared and its basic strength reached 26.5 measured by indicators according to Hammett scale. The catalytic activity of Eu₂O₃/Al₂O₃ was evaluated for the transesterification of soybean oil with methanol to biodiesel in the fixed bed reactor and under atmospheric pressure. The results show that Eu₂O₃/Al₂O₃ is an excellent catalyst for the transesterification of soybean oil, and the conversion of soybean oil can reach 63.2% at 70 °C for 8 h.     

Laser machining of Al2O3-ZrO2 (3%Y2O3) eutectic composite

In this work we present the study of the interaction between NIR pulsed laser and Al₂O₃-ZrO₂ (3%Y₂O₃) eutectic composite. The effect produced by modifying the reference position as well as the working conditions and laser beam features has been studied when the samples are processed by means of pulse bursts.The samples were obtained by the laser floating zone technique using a CO₂ laser system. The laser machining was carried out with a Q-switched Nd:YAG laser at its fundamental wavelength of 1064 nm with pulse-widths in the nanosecond range.Geometric dimensions, i.e. ablated depth, machined width and removed volume as well as ablation yield of the resulting holes have been studied. We have described and discussed the morphology, composition and microstructure of the processed samples.     

Skeletal isomerization of 1-butene over ferrierite and ZSM-5 zeolites: influence of zeolite acidity

Three ferrierite (FER) and five ZSM-5 (MFI) zeolites with SiO₂Al₂O₃ ratio ranging from 27 to 2000 are tested as catalysts for the skeletal isomerization of 1-butene at 350–450°C and atmospheric total pressure in order to study the influence of acidity and pore structure of zeolite on conversion and selectivity. The catalytic and NH₃ temperature-programmed desorption results from FER and MFI catalysts with the same SiO₂/Al₂O₃ ratio reveal that the pore structure of FER zeolite rather than its acidity may play an important role in achieving high selectivity for the skeletal isomerization of 1-butene to isobutene.     

Selective synthesis of mixed alcohols from syngas over catalyst Fe2O3/Al2O3 in slurry reactor

The Fe₂O₃/Al₂O₃ catalyst was studied to selectively synthesize mixed alcohols from syngas in a continuously stirred slurry reactor with the oxygenated solvent Polyethylene Glycol-400 (PEG-400). The selectivity of mixed alcohols in the products reached as high as 95 wt.% and the C₂₊ alcohols (mainly ethanol) was more than 40 wt.% in the total alcohol products at the reaction conditions of 250 °C, 3.0 MPa, H₂/CO = 2 and space velocity = 360 ml/g_cat h. The hydrogen temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) measurements of the catalyst confirmed that the FeO phase was responsible for the high selectivity to mixed alcohols in the process. And the oxygenated solvent PEG-400 was also necessary for the selective synthesis of mixed alcohols in the reaction system.     

Hydrogen production by steam reforming of LNG over Ni/Al2O3-ZrO2 catalysts: Effect of ZrO2 and preparation method of Al2O3-ZrO2

An Al₂O₃-ZrO₂ support was prepared by grafting a zirconium precursor onto the surface of commercial γ-Al₂O₃. A physical mixture of Al₂O₃-ZrO₂ was also prepared for the purpose of comparison. Ni/Al₂O₃-ZrO₂ catalysts were then prepared by an impregnation method, and were applied to the hydrogen production by steam reforming of liquefied natural gas (LNG). The effect ZrO₂ and preparation method of Al₂O₃-ZrO₂ on the performance of supported nickel catalysts in the steam reforming of LNG was investigated. The Al₂O₃-ZrO₂ prepared by a grafting method was more efficient as a support for nickel catalyst than the physical mixture of Al₂O₃-ZrO₂ in the hydrogen production by steam reforming of LNG. The well-developed tetragonal phase of ZrO₂ and the high dispersion of ZrO₂ on the surface of γ-Al₂O₃ were responsible for the enhanced catalytic performance of Ni/Al₂O₃-ZrO₂ prepared by way of a grafting method.     

Improvement of coke resistance of Ni/Al2O3 catalyst in CH4/CO2 reforming by ZrO2 addition

This work investigates the improvement of Ni/Al₂O₃ catalyst stability by ZrO₂ addition for H₂ gas production from CH₄/CO₂ reforming reactions. The initial effect of Ni addition was followed by the effect of increasing operating temperature to 500–700 °C as well as the effect of ZrO₂ loading and the promoted catalyst preparation methods by using a feed gas mixture at a CH₄:CO₂ ratio of 1:1.25. The experimental results showed that a high reaction temperature of 700 °C was favored by an endothermic dry reforming reaction. In this reaction the deactivation of Ni/Al₂O₃ was mainly due to coke deposition. This deactivation was evidently inhibited by ZrO₂, as it enhances dissociation of CO₂ forming oxygen intermediates near the contact between ZrO₂ and nickel where the deposited coke is gasified afterwards. The texture of the catalyst or BET surface area was affected by the catalyst preparation method. The change of the catalyst texture resulted from the formation of ZrO₂–Al₂O₃ composite and the plugging of Al₂O₃ pore by ZrO₂. The 15% Ni/10% ZrO₂/Al₂O₃ co-impregnated catalyst showed a higher BET surface area and catalytic activity than the sequentially impregnated catalyst whereas coke inhibition capability of the promoted catalysts prepared by either method was comparable. Further study on long-term catalyst stability should be made.     

Growth evolution of rapid grown aligned carbon nanotube forests without water vapor on Fe/Al2O3/SiO2/Si substrate

This paper presents the growth evolutions in terms of the structure, growth direction and density of rapid grown carbon nanotube (CNT) forests observed by scanning and transmission electron microcopies (SEM/TEM). A thermal CVD system at around 700 °C was used with a catalyst of Fe films deposited on thin alumina (Al₂O₃) supporting layers, a very fast raising time to the growth temperature below 25 °C/s, and a carbon source gas of acetylene diluted with hydrogen and nitrogen without water vapor. Activity of Fe catalyst nanoparticles was maintained for 5 min during CVD process, and it results in CNT forests with heights up to 0.6 mm. SEM images suggest that the disorder in CNT alignment at the initial stage of CNTs plays a critical role in the formation of continuous CNT growth. Also, the prolonged heating process leads to increased disorder in CNT alignment that may be due to the oxidation process occurring at the Fe nanoparticles. TEM images revealed that both double- and few-walled CNTs with diameters of 5-7 nm were obtained and the CNT density was controlled by thickness of Fe catalytic layer. The number of experiments at the same conditions showed a very good repeatability and reproducibility of rapid grown CNT forests.     

Matrix–filler interactions in polysilazane-derived ceramics with Al2O3 and ZrO2 fillers

Interactions between a poly(vinyl)silazane and Al₂O₃ or Y₂O₃-stabilised ZrO₂ fillers were studied during the fabrication of polysilazane-derived bulk ceramics in order to investigate the influence of oxide fillers on resulting properties. Specimens were produced by coating of the filler powders with the polysilazane, warm-pressing of the resulting composite powders, and pyrolytic conversion in flowing N₂ at various temperatures between 1000 °C and 1400 °C. Significant differences in densification were observed, depending on the filler used. Reactions between the polysilazane-derived matrix and Al₂O₃ or ZrO₂ at temperatures ≥1300 °C resulted in the formation of Si₅AlON₇ or ZrSiO₄, respectively. Reactivity in the polysilazane-derived component was a result of SiO₂ contamination caused primarily by adsorbed species on the filler particle surface. Knowledge of polysilazane/filler interface processes is found to be decisive for the prediction of properties such as shrinkage and porosity, which heavily influence performance of a material.     

Influence of MgO on the formation of Ca3SiO5 and 3CaO·3Al2O3·CaSO4 minerals in alite-sulphoaluminate cement

The influence of MgO on the formation of Ca₃SiO₅ and 3CaO·3Al₂O₃·CaSO₄ minerals in alite-sulphoaluminate cement is reported in this paper. The results show that adding a suitable amount of MgO can lower the clinkering temperature, promote the formation of Ca₃SiO₅ and 3CaO·3Al₂O₃·CaSO₄ minerals, and help in the coexistence of the two minerals in the clinker. MgO may obviously decrease the formation of Ca₃Al₂O₆, and increase the SiO₂ content incorporated into the interstitial phase.     

Mechanical properties of Al2O3-Cr2O3/Cr3C2 nanocomposite fabricated by spark plasma sintering

The fine grains of Al₂O₃-Cr₂O₃/Cr-carbide nanocomposites were prepared by employing recently developed spark plasma sintering (SPS) technique. The initial materials were fabricated by a metal organic chemical vapor deposition (MOCVD) process, in which Cr(CO)₆ was used as a precursor and Al₂O₃ powders as matrix in a spouted chamber. The basic mechanical properties like hardness, fracture strength and toughness, and the nanoindentation characterization of nanocomposites such as Elastics modulus (E), elastic work (W_e) and plastic work (W_p) were analyzed. The microstructure of dislocation, transgranular and step-wise fracture surface were observed in the nanocomposites. The nanocomposites show fracture toughness of (4.8 MPa m^1/2) and facture strength (780 MPa), which is higher than monolithic alumina. The strengthening mechanism from the secondary phase and solid solution are also discussed in the present work. Nanoindentation characterization further illustrates the strengthening of nanocomposites.