The influence of mordenite characteristics in mordenite mixed with alumina on cracking of vacuum gas oil

Catalytic cracking of vacuum gas oil has been investigated at 500 ‡C over mixed catalysts in a micro-activity tester. The catalyst consists of mordenite treated by either HCl/steam or HF and alumina prepared at pH of 9.5 or 7.8. The catalysts retaining mordenite in which SiO₂/Al₂O₃ weight ratio ranged from 15 to 20 show the max-imum activity and selectivity for gasoline. Both the activity and selectivity for gasoline seem to depend strongly on both acid strength of mixed catalysts and mesopore volume of the mordenite. It is found, however, that the selectivity of kerosene+diesel in liquid product as well as the yield of aromatics in gasoline are influenced more by mesopore volume of mordenite than by acid properties of mordenite in the catalyst of mordenite/alumina.     

Butane dehydrogenation over Pt/alumina: activation, deactivation and the generation of selectivity

The dehydrogenation of butane over a Pt/alumina catalyst has been studied using pulse-flow techniques. The selectivity to butenes is generated as carbonaceous material is deposited. The final catalyst is sensitive to whether reduction has taken place in hydrogen or butane, with the more effective dehydrogenation catalyst being generated from a hydrogen reduction.     

I: Dispersibility of robust alumina particles in non-aqueous solution

This article presents the preparation of well dispersed alumina slurries containing relatively large alumina particles that can withstand accelerated weather conditions. Besides using conventional dispersants such as phosphate esters and menhaden fish oil, dispersants widely used in the surface coatings industries such as Disperbyk 110 and Triton X 100 have also been employed. However, sedimentation tests, sediment density, viscosity and gloss measurements indicate the failure of the anionic dispersants as well as menhaden fish oil to disperse the alumina particles in non-aqueous medium. Instead the binder polyvinyl butyral itself acts as the best dispersant. The well dispersed alumina slurry is stabilized in the presence of a commercially available rheology modifier, Bentone SD2 for a period of 144 h at 60 °C. The rheological behavior of the aged sample was studied under various conditions. Although a rise in viscosity of the suspension was observed when the slurry was exposed to accelerated weather conditions, a lower shear thinning index and higher gloss values indicate a better dispersion state with aging.     

Integrated preparation of alumina microfiltration membrane with super permeability and high selectivity

A dual-layer alumina microfiltration membrane with super permeability and high selectivity was prepared by co-sintering the membrane and the support. Silica sol as sintering aid for the supports can also promote adhesion between supports and membranes. Tape-casting technique was introduced here to form the pre-membranes which were directly transfer-coated on the green support bodies. The optimum co-sintering conditions and the effects of organic agent content and membrane thickness on the membrane performance were comprehensively investigated. The optimized ceramic membrane had an average pore size of 249 nm and a water permeance of 5040 Lm⁻² h^-1 bar^-1 after co-sintering at 1300 °C for 2 h, which also exhibited a rejection rate of 96.2% for the carbon ink with an average particle size of 237 nm. This work provides a new method for efficient and low-cost preparation of high-performance ceramic membranes.     

偏高岭土超细粉对中间包永久衬用高铝浇注料性能的影响

以8～5mm、5～3mm、≤3mm的矾土为骨料,保持颗粒与细粉质量比为65:35不变,研究了用d50=15.91μm,加入量(w)为4%、6%、8%的偏高岭土超细粉,分别取代d50=1.75μm,加入量(w)为1%、2%、3%的Al2O3微粉后,中间包永久衬用高铝质浇注料施工性能、机械强度以及矿物组成的变化。结果认为:用偏高岭土超细粉完全可以取代Al2O3微粉生产莫来石质中间包永久衬用浇注料,添加偏高岭土超细粉的浇注料的流动性、粘聚性、保水性等明显优于加入Al2O3微粉的,且经1400℃煅烧后的机械强度较高;XRD分析表明,以8%偏高岭土超细粉完全取代Al2O3微粉后,试样于1400℃3h烧后的莫来石相含量最高,且其各项性能指标与中间包永久衬要求相一致。     

Nucleation and growth of Pd clusters in mordenite

The nucleation and growth of Pd clusters in mordenite were investigated using in situ extended X-ray absorption fine structure (EXAFS) spectroscopy and Fourier transform infrared (FTIR) spectroscopy of absorbed CO. Calcination of [Pd(NH₃)₄]²⁺-exchanged mordenite at 350°C in O₂ results in decomposition of the amine complex and formation of square-planar Pd²⁺ oxo species within the mordenite pores. Reduction of these species at 150°C in H₂ yields Pd clusters with an average nuclearity of 3. On an average two 2.22 Å Pd-O bonds are associated with each Pd₃ cluster; we infer that this interaction serves to anchor the clusters within the pores. After reduction at 150°C, the FTIR spectrum of irreversibly adsorbed CO is indicative of a mixture of Pd⁺, Pd^δ+, and Pd⁰ carbonyl species. Reduction at 350°C produces larger intrazeolitic Pd clusters (average nuclearity of 6) that exhibit only a weak interaction with the mordenite, as evidenced by their facile aggregation in the presence of CO at 30°C. Reduction at 450°C yields large 20 Å Pd clusters that we infer are located on external mordenite surfaces or locally disrupt the intracrystalline structure.     

Stabilizing effect of the carbon shell on phase transformation of the nanocrystalline alumina particles

Intensive phase transformations of alumina are known to occur at temperatures above 1000 °C. In the present work, high temperature behaviour of pure Al₂O₃ and the carbon coated Al₂O₃@C sample with core-shell structure was comparatively studied using low-temperature nitrogen adsorption, transmission electron microscopy, powder X-ray diffraction (XRD) analysis and solid-state nuclear magnetic resonance (NMR). The solid-state NMR ²⁷Al method has allowed us to identify and estimate the concentration of all phases appeared during the transformation of pseudoboehmite γ-Al₂O₃ into corundum α-Al₂O₃. The data obtained correlate well with the results of XRD analysis and low-temperature nitrogen adsorption. It is shown that the deposition of carbon coating with formation of core-shell Al₂O₃@C system stabilizes the size of oxide core and prevents the formation of corundum phase until the temperatures of 1350–1400 °C, which are close to the temperature of carbothermal reduction of alumina. The stabilization of the size of the oxide core nanoparticles was considered as a main factor preventing the formation of corundum phase at high temperatures. At the same time, the carbon coating does not affect the phase transformation of γ-Al₂O₃ to δ-Al₂O₃.     

Effect of carbon contamination on the sintering of alumina ceramics

The present work aimed with the carbon contamination in alumina ceramics and its influence on sinterability of alumina in low vacuum and atmospheres of argon and nitrogen. The commercially available alumina was coated with carbon and sintered at different atmospheres to investigate the effect of carbon presence on alumina sintering behaviour. The sintering conditions were: heating/cooling rates 5 °C/min and 1.7 °C/min until the maximum temperature of 1400 °C and a dwell time of 2 h. The microstructure of the samples was investigated from fracture and surface, prior to polishing, chemical or thermal etching. The non-densified (porous) surface layer was found in the samples sintered in nitrogen and vacuum, however, sintering in argon atmosphere showed a negligible effect on the surface. The core of investigated specimens exposes a transgranular/intergranular fracture mode and is dense in all cases. In the case of vacuum sintering, the strong carbon diffusivity was also noticeable by the dark grey color of the samples. Interestingly, the formation of aluminium nitride took place during sintering of carbon coated alumina samples in a nitrogen atmosphere at 1400 °C. The thickness of the reactive porous layer was approximately 15 μm beneath the surface. Such a porous layer is inappropriate to the desired features of final ceramic products. Presented results lead to better understanding of the sintering behaviour of ceramic and to suitable selecting of the set-up by densification conditions.     

Effect of binder on the structure and mechanical properties of lightweight bubble alumina ceramic

The effect of binders such as ammonium aluminum sulphate, phosphoric acid and composite binder on the properties of lightweight bubble alumina ceramic was studied. The composite binder was composed of ammonium aluminum sulphate and phosphoric acid. Ammonium aluminum sulphate solution can improve compressive strength of alumina bubbles effectively but can not improve that of lightweight bubble alumina ceramic due to the fewer nano-alumina powders in situ decomposed of ammonium alumina sulphate. Trans-ball fractures occurred in thermal shock test. Phosphoric acid solution can improve compressive strength of alumina bubble ceramic because of promoting sintering properties of aluminum phosphate in situ produced by phosphoric acid and alumina component during sintering but decrease that of alumina bubbles. Along-ball fractures occurred in thermal shock test. The composite binder combined with the advantages of ammonium alumina sulphate and phosphoric acid and improved the compressive strength of both alumina bubbles and lightweight bubble alumina ceramic, and effectively reduce the amount of the binders and lower the product cost. At the sintering temperature of 1700 °C, with composite ammonium alumina sulphate and phosphoric acid as binder, the density of lightweight bubble alumina ceramic was between 1.20 and 1.60 g/cm³, and the compressive strength was 18-42 MPa.     

Influence of anionic stabilization of alumina particles in 2-propanol medium on the electrophoretic deposition and mechanical properties of deposits

The ceramic dispersions were prepared using 0.85, 1.70, 4.25, 12.75 or 21.25 wt.% of monochloroacetic, dichloroacetic or trichoroacetic acid, 15 wt.% alumina and 2-propanol. The mechanism of anionic stabilization in 2-propanolic media was described. Alumina green bodies were prepared from the stable dispersion via electrophoretic deposition (EPD). It was found that increasing dispersion conductivity significantly influenced the EPD yields. The most effective electrophoretic depositions were performed from dispersions with conductivity in range 4.0–5.3 × 10⁻⁴ S m⁻¹. Deposits with the highest green density were prepared from the dispersion stabilized by trichloroacetic acid. This behavior was explained by low voltage drop during deposition. The surface roughness was high at low dispersion conductivity and with increasing acid concentration in dispersion the surface of deposits was smoother. The mechanism of particle arrangement in deposit was discussed. Influence of stabilizer amount in the dispersion on the hardness and fracture toughness was described.     

NO ions as IR probes for the location of OH groups and Na ions in main channels and side pockets of mordenite

NO⁺, generated from NO and O₂, is an infrared probe for the differentiation of Brønsted sites in the main channels and side pockets of mordenites, and for the location and accessibility of sodium ions in the structure. Na⁺ ions in cationic positions in the main channels are replaced by NO⁺, and sodium nitrate is formed. The band assignment was checked by isotopic experiments.     

Effect of the incorporation of ETS-10 into alumina on metal-support interactions and hydrodesulfurization activity

Effect of the incorporation of ETS-10 into alumina on metal-support interactions was firstly studied systematically by the techniques of DSC, TG, XRD, DRS and LRS. The results show that the introduction of ETS-10 substantially improves metal-support interactions, inhibits the formation of inactive aluminium tungstate species and nickel spinel, and stimulates more polymeric tungsten species formation, which facilitates the promoting effect of nickel on tungsten and contributes to a noticeable increase in HDS activity.     

Activity and selectivity of high-silica mordenites in the disproportionation of ethylbenzene

The disproportionation of ethylbenzene was investigated over high-silica zeolites prepared by both direct crystallization and dealumination. It was found that dealumination increases the rate of the reaction and improves the life time of the mordenite catalysts. It was shown, however, that the catalytic performance of dealuminated mordenites is not unambiguously related to the number of the Al atoms per unit cell, N^F_Al, remaining in the framework. Rather, it depends on the method of dealumination. Catalysts prepared via heat treatment of NH₄-mordenites and subsequent acid leaching proved to be superior to those having the same N^F_Al but were obtained by acid leaching of Na–mordenite. A mordenite sample prepared through the former method and possessing a Si/Al ratio of, e.g., 11.5 exhibited a rather high activity and catalytic stability compared to materials obtained via the second procedure. The differences in the catalytic performance of mordenites produced through different methods are discussed in terms of microporosity and both density and strength of acidic sites. In particular, it is inferred that the so-called isolated (0-NNN) Al atoms play an important role. The conditions for preparation of mordenites are outlined that are favorable for the enhanced formation of p-diethylbenzene.     

Effect of residual stresses to the crack path in alumina/zirconia laminates

Laminates with alternating layers are well known from nature. The strongly bonded alumina/zirconia (Al₂O₃/ZrO₂) layers can combine high fracture resistance with high strength and stiffness when properly tailored. The presence of compressive residual stresses formed in Al₂O₃ layers can suppress and deflect cracks propagating through the layers. The crack path is governed by both the elastic properties and the internal stress field of individual layers. The laminates with various layer-thickness ratios ranging from 0.1 to 3 were used to investigate the effect of residual stresses and influence of crack formation pattern on the crack path development. The indentation surface cracks observed in various alumina-zirconia laminates exhibit the same crack deflection independently on the level of internal stresses. The crack deflection observed on the fracture surfaces of bending specimens was related to the indentations cracks. The complicated crack path was explained experimentally by 3D reconstruction with the support of numerical simulations.     

Effect of the anodization voltage on the pore-widening rate of nanoporous anodic alumina

ABSTRACT: A detailed study of the pore-widening rate of nanoporous anodic alumina layers as a function of the anodization voltage was carried out. The study focuses on samples produced under the same electrolyte and concentration but different anodization voltages within the self-ordering regime. By means of ellipsometry-based optical characterization, it is shown that in the pore-widening process, the porosity increases at a faster rate for lower anodization voltages. This opens the possibility of obtaining three-dimensional nanostructured nanoporous anodic alumina with controlled thickness and refractive index of each layer, and with a refractive index difference of up to 0.24 between layers, for samples produced with oxalic acid electrolytes.     

Optimal design conditions for dehydrogenation of cyclohexane in a membrane reactor

The design variables of a membrane reactor, such as the permeation rate through the membrane and catalyst loading in the membrane, have received little attention in comparison with the operating conditions. A non-dimensionalized model for a membrane reactor was developed to account for the effects of permeation rate and catalyst loading. The increased permeation rate did not always increase the exit conversion and there existed a maximum point of exit conversion. At isothermal conditions, the exit conversion was saturated as catalyst loading was increased; however, when the reactor was under non-isothermal condition along the axial direction, there existed an optimum catalyst loading at which the exit conversion was maximum. With this model, the optimal configuration of permeation rate and catalyst loading could be determined.     

Cr2O3对MgO-Al2O3系浇注料性能的影响

研究了氧化铬的引入方式及引入量对钢包渣线用MgO-Al2O3系浇注料性能的影响.结果表明,以工业氧化铬方式引入Cr2O3比以镁铬尖晶石方式引入Cr2O3对材料的热震稳定性更有利,Cr2O3的引入量控制在2%～4%时,材料的抗渣性可以得到显著改善.     

Synthesis and thermal properties of phase‐change microcapsules incorporated with nano alumina particles in the shell

Novel phase‐change microcapsules with paraffin as core and melamine‐formaldehyde (MF) resin as shell were synthesized through in situ polymerization, in which nano alumina (nano‐Al₂O₃) particles were dispersed in the shell by mixing nano‐Al₂O₃ with MF prepolymer solution using the direct addition method (i.e., adding nano‐Al₂O₃ into the MF prepolymer solution directly) and the predispersed addition method (i.e., predispersing the nano‐Al₂O₃ homogenously in water under the assistance of dispersant and wetting agents before mixing with the MF prepolymer). Scanning electron microscope experiments demonstrated that the predispersed addition method yielded the microcapsules having the better dispersion and less self‐agglomeration of alumina, compared to the direct addition method. Fourier transform infrared spectroscopy, energy dispersive X‐ray spectroscopy, and electron backscatter diffraction imaging confirmed that the nano‐Al₂O₃ particles were successfully incorporated in the shell by the predispersed addition method. The phase change behavior of microcapsules incorporated with different contents (up to 12.7% relative to the microcapsule) of nano‐Al₂O₃ particles in the shell was investigated by differential scanning calorimeter. The results revealed that the encapsulation efficiency for this kind of novel microcapsules was >77% and the incorporation of nano‐Al₂O₃ in the shell affected the phase change temperature. Thermal gravimetric analysis indicated that the addition of nano‐Al₂O₃ improved the thermal stability of microcapsules remarkably. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Template-directed synthesis of porous alumina particles with precise wall thickness control via atomic layer deposition

Highly porous alumina particles with precise wall thickness control were synthesized by atomic layer deposition (ALD) of alumina on highly porous poly(styrene-divinylbenzene) (PS-DVB) particle templates. Alumina ALD was carried out using alternating reactions of trimethylaluminum and water at 33 °C. The growth rate of alumina was ∼0.3 nm per coating cycle. The wall thickness can be precisely controlled by adjusting the number of ALD coating cycles. Thermo-gravimetric analysis, X-ray diffraction, nitrogen adsorption, scanning electron microscopy, and transmission electron microscopy were used to characterize the fabricated porous alumina particles. The effect of number of ALD coating cycles and calcination temperature on the mesoporous structure of the alumina particles was investigated. γ-Alumina was formed at temperature above 600 °C. Porous alumina particles with a surface area of 80-100 m²/g were obtained and thermally stable at 800 °C. The pore volume of the porous particles can be as high as 1 cm³/g after calcination at 800 °C. Such porous alumina particles may find wide application in nanotechnology and catalysis.     

尖晶石对凝胶结合氧化铝空心球浇注料性能的影响

以5～3mm、3～2mm、2～1mm、1～0.2mm粒度氧化铝空心球为原料,引入二氧化硅微粉制成凝胶结合氧化铝空心球浇注料,研究了预合成镁铝尖晶石对凝胶结合氧化铝空心球浇注料性能的影响。用各种耐火制品检测设备和仪器对引入不同量尖晶石的试样性能进行了检测。结合氧化镁-氧化铝-二氧化硅相图进行理论分析,结果发现:尖晶石的引入促进了浇注料中刚玉相的烧结,提高了凝胶结合氧化铝空心球浇注料的常温耐压强度和显气孔率,降低了浇注料的体积密度。尖晶石对凝胶结合氧化铝空心球浇注料基质具有强化作用,有利于提高浇注料的热震稳定性