Pseudoboehmite Research Articles

Aluminium hydro(oxide)–based (AO) adsorbent for defluoridation of drinking water: Optimisation, performance comparison, and field testing

In this study, the performance of different aluminium hydroxide.based adsorbents was compared in terms of fluoride adsorption capacity, potential for repetitive regeneration, surface acidity and surface site concentrations. The adsorbents were aluminium hydro(oxide) (AO), activated alumina (AA), and pseudoboehmite (PB). The AO adsorbent was synthesised at different OH:Al ratios to optimise the fluoride adsorption capacity. The AO was pilot tested in a rural community in the Ethiopian Rift Valley where groundwaters are heavily enriched with fluoride. The maximum fluoride uptake was achieved for the AO adsorbent synthesised at OH:Al ratios between 2.5 and 2.7. The fluoride adsorption capacity of the adsorbents determined from mini-column studies was found to be 10.6, 1.9, and 2.4 mg/g for AO, AA, and PB, respectively. This significant difference in fluoride adsorption capacity is strongly related to the surface acidity and surface site concentration. The surface acidity (1.57 meq/g) and surface site concentration (0.74 meq/g) for AO is higher than that for AA and PB. The elemental composition analysis showed that AO has a lower % Al2O3 content than AA and PB, but higher sulphate (19.4%) and iron (2.2%) content. High resolution 27Al Magic Angle Spinning Nuclear Magnetic Resonance (27Al MAS NMR) spectra of AO, AA, and PB were recorded, to analyse the coordination geometry of solid Al species and the results showed that aluminium is coordinated octahedrally and tetrahedrally in all cases. Regeneration experiments showed that AA and PB can be regenerated for more than 3 cycles, whereas the potential for regeneration of AO for more than 3 cycles is limited. The results from a community defluoridation plant showed that fluoride in the feed water (8.10 mg/.) is removed below 0.1 mg/.. The average adsorption capacity was determined to be 2.11 mg/g based on continuous field monitoring results obtained until the fluoride content in the treated water exceeded the breakthrough value of 1.5 mg/.. No major operational problems and complaints from the beneficiaries were experienced during operation. Keywords : fluoride, adsorption, surface acidity, regeneration, defluoridation, Ethiopia

Potassium-Promoted γ-Alumina Adsorbent from K2CO3 Coagulated Alumina Sol for Warm Gas Carbon Dioxide Separation

This paper provided a practical synthesis method of K-promoted γ-alumina for CO2 precombustion capture integrating adsorbent pelletting and catalytic active component promotion into one single process. The precursor of the absorbent, K-promoted pseudo-boehmite (PB), was synthesized from alumina sol and K2CO3 powder by mixing, aggregating, drying, and aging. Potassium-promoted γ-alumina was obtained after calcination at 400 °C from K-promoted PB. Characteristic crystallines of several stages of products in the synthesis process have been detected by X-ray diffraction. The optimal Al:K ratio in view of CO2 capacity and cyclic performance of K-promoted γ-alumina was obtained by a thermal gravimetric analyzer. The optimal ratio of K-promoted γ-alumina showed a capacity of 0.67 mmol/g (dry base) for the first cycle and 0.34 mmol/g (wet base) after 30 pressure swing adsorption (PSA) cycles at 300 °C. K-promoted γ-alumina adsorbent could be favorable for a low energy penalty precombustion CO2 capture application. It showed a variety of advantages such as low adsorption heat, good mechanical strength, low cost in synthesis, and fair stable capacity.

The effect of hydration layers on the anodic growth and on the dielectric properties of Al2O3 for electrolytic capacitors

Hydrous films were grown on high purity and cubicity Al foils for electrolytic capacitors in deionized water, ethylene glycol–deionized water and glycerol–deionized water at different immersion times. According to X-ray diffraction patterns the hydration treatment allowed growing a pseudo boehmite layer on Al surface whose morphology is appreciably affected by the bath composition. Capacitance measurements and photoelectrochemical findings suggest that a more compact barrier layer forms during the immersion in alcohol containing solutions. The hydration in water allowed saving energy and preparing more blocking oxide films. The beneficial effect of hydration in hot water on the specific capacitance was evidenced only for films formed at 300V due to the crystallization of amorphous alumina in γ′-Al2O3.

Regenerable granular carbon nanotubes/alumina hybrid adsorbents for diclofenac sodium and carbamazepine removal from aqueous solution

A novel granular carbon nanotubes (CNTs)/alumina (Al2O3) hybrid adsorbent with good sorption and regeneration properties was successfully prepared by mixing CNTs with surfactant Brij 35 and pseudo boehmite, followed by calcining to remove surfactant and form porous granules. Alumina binder increased the mechanical strength, hydrophilicity and porosity of the granular adsorbent, while the dispersed CNTs in the granular adsorbent were responsible for the sorption of diclofenac sodium (DS) and carbamazepine (CBZ). Scanning electron microscopy (SEM) showed that the CNTs and Al2O3 were mixed well and the porous structure was formed in the granular adsorbent. The high surface area and appropriate pore size of granular CNTs/Al2O3 adsorbent were favorable for sorption. The sorption of DS decreased with increasing solution pH, while pH had little effect on CBZ sorption. The maximum sorption capacities of CBZ and DS on the CNTs/Al2O3 adsorbent were 157.4 and 106.5 μmol/g according to the Langmuir fitting. Moreover, the spent CNTs/Al2O3 adsorbent can be thermally regenerated at 400 °C in air due to the thermal stability of CNTs. The removal of CBZ and DS changed a little in the initial reuse cycles and then kept relatively constant until tenth cycles. The adsorbed CBZ and DS were decomposed in the regeneration process. This regenerable adsorbent may find potential application in water or wastewater treatment for the removal of some micropollutants such as pharmaceuticals.

高比表面积Al2O3-TiO2二元气凝胶小球的制备

以拟薄水铝石和水合硫酸氧钛为前驱体，水为溶剂，采用溶胶–凝胶、烃氨成球法、老化和控制干燥制备出大比表面积的AlO2-TiO2复合气凝胶小球。研究其理化性质并考察了不同铝钛组成及温度对孔结构和酸量的影响。采用了SEM、XRD、FT-IR、NMR、N2吸附–脱附法、NH3-TPD等手段对所制得的复合氧化物进行了表征。结果显示，复合氧化物中TiO2为锐钛矿型，Al2O3为无定形。通过混合溶胶共水解缩聚及老化和控制干燥，使不同铝/钛比的二元气凝胶小球的比表面积均达到200 m2/g以上，总酸量达到0.8 mmol NH3/g以上。不同铝/钛比的二元气凝胶小球比表面积和酸量相近，孔径可通过铝/钛比调整。 Crack-free and high surface area mesoporous alumina-titania binary aerogel beads have been synthesized by sol-gel technology, the ball dropping method (BDM), extended aging and gradient drying method with pseudo boehmite and dehydrate titanyl sulfate as precursors and water as solvent. The effects of composition and calcination temperature on pore structure and acid amounts have been investigated and discussed. The binary aerogel beads have been charac-terized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier-transform infrared spectros-copy (FT-IR), solid state nuclear magnetic resonance (NMR), nitrogen adsorption/desorption analysis and ammonia- temperature programmed desorption (TPD). The obtained aerogel beads show surface area of 200 m2/g and acid amounts of 0.8 mmol NH3/g respectively. The binary aerogel beads with different constitutes show similar specific sur-face area and acid amounts. The pore size of aerogel beads can be modified by changing composition and calcination temperature.

Preparation of Pseudoboehmite with a Large Pore Volume and a Large Pore Size by Using a Membrane-Dispersion Microstructured Reactor through the Reaction of CO2 and a NaAlO2 Solution

In this work, a membrane-dispersion microstructured reactor was specially designed to prepare PB (pseudoboehmite) with a large pore volume and a large pore size through the reaction of CO2 and an aqueous solution of NaAlO2. Tiny crystals of PB and a suitable template are necessary for generating large pore diameter and large pore volume. In this reactor, the tiny crystals could be obtained by increasing the mass transfer rate between the gas phase and the liquid phase through dispersing the CO2 gas into many microbubbles, and these microbubbles could act as a template to increase the pore volume. The effects of the final pH of the aqueous solution, the concentrations of raw materials, and the flow rate of the gas phase on pore properties of products were investigated. The results showed that when the final pH of the aqueous solution was between 10.5 and 9.4, pure PB could be obtained, and the crystal size of PB was about 2.3 nm. In addition, the specific surface area, the pore volume, and the average pore...

A Pseudoboehmite-Silane Hybrid Coating for Enhanced Corrosion Protection of AA2024-T3

This work reports the performance of pseudoboehmite (PB)-silane hybrid coatings for the corrosion protection of AA2024-T3. A survey of the coating pretreatment and treatment steps was undertaken to reveal the electrochemical impact of such treatments on AA2024-T3 and its constituents, with testing also done on model microstructural analogs including Al–4Cu, , and . The hybrid coating performs very well in immersion and salt-spray conditions. The protective effect of the PB pretreatment is not additive but synergistic. PB surface layers could be integrated as a precursor to subsequent coatings owing to the functionality they can impart to the surface.

Influence of precursors on the catalytic activity of alumina for bio-ethanol dehydration in microchannel reactors

In this paper, the catalytic activity of alumina for bio-ethanol dehydration was studied in a microchannel reactor. Five catalysts were prepared from precursors with different ratios of AlOOH (pseudo boehmite) and Al(OH)3 (bayerite). The physicochemical properties of catalysts were characterised by X-Ray Diffraction (XRD) and Temperature Programmed Desorption (TPD). The influence of reaction temperature and space velocity was investigated. The results show that the catalyst prepared from precursor with AlOOH 46.3 mol% has the highest ethanol conversion and ethylene selectivity. An ethylene yield of 18.28 g/(gcat⋅h) can be achieved, implying that the dehydration process can be intensified using microchannel reactors.

Performance of La-Ba Co-modified Alumina Prepared by Peptizing Method

La-Ba co-modified alumina was prepared from two kinds of pseudo boehmite and HNO_3 as peptizer by peptizing method.The structure and surface property of the alumina were characterized by XRD,BET surface area analyzer,NH_3-temperature programmed desorpfion and NO_2-temperature programmed desorption technology.XRD results showed thatγ-Al_2O_3 phase existed in all the modified alumina samples after calcination at 1273 K.A little BaCO_3 was generated when content of BaO was increased to 14%(w).BET results showed that both of 5%(w) La_2O_3- modified and 5% La_2O_3-8%BaO co-modified alumina (Ba-8) samples exhibited larger specific surface area and pore volume after calcination at 1273 K.N_2 adsorption and desorption isotherms of all alumina exhibited that their surface pore structure was slit-shape and ink-shape pores,pore diameter distribution of Ba-8 was broader and centered between 5 and 10 nm,and other samples centered at 10 nm.NH_3-TPD results indicated that the larger the BaO doping concentration,the less the acidic amount was.At the same time,surface acidity of alumina apparently became weak. NO_2-TPD results showed that BaO doped alumina adsorbed more NO_2 than La_2O_3 doped,sample Ba-8 adsorbed the most NO_2.As sample Ba-8 simultaneously exhibited good textural properties,proper surface acidic amount,acidity and stronger NO_2 adsorption capacity,it had the best catalytic performance when it was used as catalyst carder.The temperatures of light-off and complete conversion of C_3H_3 were 526 K and 593 K,respectively.

Influences of processing techniques of the H 2O 2-precipitated pseudoboehmite on the structural and textural properties of γ-Al 2O 3

Influences of three post-precipitation techniques, n-butanol azeotropic distillation, ethanol washing and water washing of the H 2O 2-precipitated pseudoboehmite (PB) from sodium aluminate (SA) solutions on the structural and textural properties of γ-Al 2O 3 upon calcination were comparatively studied. The first two processing techniques not only yield folded and swollen sheet-like pseudoboehmite and γ-Al 2O 3 nanofibres, but also increase their macro-mesopore volume and specific surface area significantly. The mechanisms for the formation of nanofibres and macro-mesopore volume induced by butoxy group or ethoxy group were also proposed. In contrast, n-butanol azeotropic distillation is more competitive for widening pores and preventing them from collapsing due to its larger n-butanol molecules, longer butoxy groups and the more complete replacement of residual water in the precipitate. The γ-Al 2O 3 from azeotropic distillation exhibits more excellent macro-mesostructure with high surface area (about 4.21 cm 3/g and 396.3 m 2/g) than those of the γ-Al 2O 3 from ethanol washing (about 2.23 cm 3/g and 222.0 m 2/g).

Synthesis of nano-fibers of aluminum hydroxide in novel rotating packed bed reactor

This paper presents a route of synthesizing nano-fibrillar aluminum hydroxide (AH) by carbonation in a novel rotating packed bed (RPB) reactor and thermal hydrolysis. Carbonation of sodium aluminate (SA) is conducted by introducing CO 2 into RPB at room temperature to form AH gel which is subsequently treated by thermal hydrolysis for an optimum time of 30 min and temperature of 85°C to yield nano-fibrillar pseudoboehmite (PB) of 1– 10 nm in diameter and 50– 300 nm in length. Factors affecting carbonation process such as high gravity level, Gas/Liquid ratio and SA solution concentration are discussed. Experimental results reveal that operating conditions have significant influences on the properties of PB and the morphology of PB is closely related to the unit structure of AH gel. The as-prepared PB is characterized by TEM and XRD and compared with those synthesized by conventional Stirred Tank Reactor (STR). Reaction time in RPB shortens for approximately a half compared with that in STR. It is proven that this route has obvious advantages over STR.

Comparison of effect of La-modification on the thermostabilities of alumina and alumina-supported Pd catalysts prepared from different alumina sources

The thermostability of La-free and La-modified aluminas derived from different alumina sources including pseudo-boehmite, aluminum sulfate, aluminum nitrate, and aluminum chloride have been studied by characterizations of BET specific surface area (BET) and X-ray powder diffraction (XRD). Further, the activity and thermal durability of monolith-supported Pd catalysts using above different alumina as washcoats for simultaneously catalytic oxidation of C3H8, C3H6 and CO have been investigated using continuous flowing reaction. The experimental results show that the oxidation activity over the alumina-supported Pd catalysts does not keep in agreement with the surface area of aluminas derived from four aluminum sources. Lanthanum modification improves the activity of all catalysts calcined over 1000°C for simultaneously catalytic oxidation of C3H8, C3H6 and CO. Alumina source plays a role on the activity and thermostability of alumina and alumina-supported Pd catalysts. The experimental results show that pseudo boehmite is the best alumina source used for catalytic oxidation at high temperature over 1000°C.

High temperature thermal stabilization of alumina modified by lanthanum species

The effects of precursor pretreatment and addition methods of lanthanum species on stabilization of alumina (surface area loss, phase transformations and high temperature interaction with lanthanum species) have been investigated by BET specific surface area measurements (BET), X-ray powder diffraction (XRD), N 2 adsorption–desorption isotherms, thermal analysis and X-ray photoelectron spectroscopy (XPS) in the range of 600–1150°C. Although powder La 2O 3, which is mechanically mixed with γ-Al 2O 3 or pseudo boehmite, can effectively retard the α phase transformation by solid phase interaction with Al 2O 3, it does not show a positive effect on retarding the loss of surface area. Compared with the direct impregnation of γ-Al 2O 3, the gelation of pseudo boehmite by acidification accelerates phase transformations and weakens the stabilizing influence of lanthanum species. At 600°C and for atomic ratio of La/Al up to 0.1 or at 1150°C and La/Al≤0.02, the lanthanum species is highly dispersed in alumina. With the increase of calcination temperature or lanthanum content, lanthanum species is present as dispersed La 2O 3, LaAlO 3 and crystalline La 2O 3. At T≤1000°C the surface area loss of alumina is mainly attributed to the sintering of particles. The follow-up loss at T>1000°C results from both sintering and phase transformations. The highly dispersed lanthanum species retard both sintering and phase transformations, and their associated surface area loss. However, the formation of LaAlO 3 mainly retards the surface area loss resulting from the α phase transformation. Having considered the purely mechanical mixing effect of additive on the surface area loss of alumina, an influence criterion of lanthanum species on retarding the surface area loss whether resulting from sintering or from α phase transformation at high temperature ≥1000°C has been proposed in this paper.

Synthesis of mesoporous zeolites and their application for catalytic conversion of polycyclic aromatic hydrocarbons

Three series of mesoporous aluminosilicate (Al-MCM-41) samples were synthesized using different aluminum sources including aluminum isopropoxide, pseudo boehmite and aluminum sulfate. Their catalytic activities were tested in the conversion of aromatic hydrocarbons including hydrocracking of 1,3,5-triisopropylbenzene, alkylation of naphthalene, and hydrogenation of naphthalene and phenanthrene. The three series of Al-MCM-41 samples behaved differently in acting as acidic catalysts and as supports. The Al-MCM-41 synthesized using aluminum isopropoxide was found to be the most promising acidic catalyst and good support for Pt catalyst.

Synthesis and Catalytic Applications of Novel Mesoporous Aluminosilicate Molecular Sieves

ABSTRACTThis paper reports on the synthesis of four series of mesoporous aluminosilicate molecular sieves (Al-MCM-41) and their catalytic applications. Four different aluminum compounds were examined as Al source in the hydrothermal synthesis of the mesoporous aluminosilicates of MCM-41 type, including pseudo boehmite (alumina), aluminum sulfate, aluminum isopropoxide, and sodium aluminate. Each Al source was examined at three different feed Si/Al ratios in the synthesis. XRD results show that there are differences in the dioo-spacings for the samples prepared with different Al sources: sodium aluminate > Al isopropoxide > Al sulfate > pseudo boehmite. Such differences reveal that Al incorporation in the framework increases in the following order: pseudo boehmite < Al sulfate < Al isopropoxide < sodium aluminate. XRD also indicates that the synthesized Al-MCM-41 samples have different crystallinity. 27Al NMR and 29Si NMR reveal that most of the Al species in the samples prepared with pseudo boehmite were present in octahedral coordination, whereas in other samples nearly all the Al species are tetrahedral (in the framework). The acid characteristics of the synthesized molecular sieves were characterized by temperature-programmed desorption of n-butylamine, and by using 1,3,5-triisopropylbenzene hydrocracking as probe reaction. The results of TPD and probe reaction clearly indicate that the Al source used for synthesis has a major impact on the acidic and catalytic properties of Al-MCM-41. The samples prepared with Al isopropoxide and sodium aluminate are better as catalysts than those with Al sulfate and pseudo boehmite. We also explored the potential of mesoporous molecular sieves as support for noble metal hydrogenation catalysts and metal sulfide-based hydrotreating catalysts. Pd and Pt-loaded mesoporous molecular sieves were prepared and applied for hydrogenation of naphthalene and phenanthrene. The results show that mesoporous molecular sieve-supported catalysts are much more active than alumina- and titania-supported catalysts. The data for dibenzothiophene hydrodesulfurization suggest that Al-MCM-41 supported Co-Mo may be effective for deep desulfurization of distillate fuels.

Synthesis of mesoporous molecular sieves: influence of aluminum source on Al incorporation in MCM-41

Three series of mesoporous aluminosilicate molecular sieves, MCM-41, with various Si/Al ratios were synthesized using different aluminum sources (aluminum isopropoxide, pseudo boehmite and aluminum sulfate). XRD analysis, temperature programmed desorption ofn-butylamine,27Al and29Si MAS NMR, and catalytic alkylation test indicated that aluminum isopropoxide is a better source for incorporating aluminum in the framework of MCM-41 type molecular sieves with better crystallinity and acid characteristics.

ギブサイトの急速加熱による熱分解および脱水生成物の性質

Gibbsite was dehydrated in a suspension heater at a high heating velocity of an order of 104°C/s. One-stage dehydration products are obtained without forming boehmite and γ-Al2O3. The crystal structure of the products changes from χ-Al2O3 to α-Al2O3 via pseudo γ-Al2O3 as the temperature of heating gas rises. The product with a surface area 300m2/g or more transforms into bayerite and pseudo boehmite by water treating for 96h at 80°C. The χ and γ-Al2O3 to α-Al2O3 phase transformation follows zero-order kinetics at the initial stage of the reaction. The dehydration products have activation energies higher than χ or γ-Al2O3. The rate of gibbsite to α-Al2O3 phase transformation in the suspension heater is much higher than that of the dehydration products in the electric furnace.