Ammonium Aluminum Carbonate Hydroxide Research Articles

Controlling the acid-base properties of alumina for stable PtSn-based propane dehydrogenation catalysts

The surface properties of catalyst supports are important in regulating the catalytic properties of heterogeneous catalysts. Herein, we studied the effect of acid-base properties of alumina on metal-support interaction and coke deposition, and investigated the stability of catalysts in propane dehydrogenation (PDH) using PtSn/Al2O3. We prepared γ-Al2O3 (A750) from ammonium aluminum carbonate hydroxide (AACH) and compared it with a commercial sample (Sasol Puralox SBA-200; P200). We loaded 0.5 wt% Pt and 0.9 wt% Sn on alumina then conducted propane dehydrogenation at 590 °C (WHSV = 5.2 h−1). PtSn/A750 and PtSn/P200 showed compatible initial activity (conversion = ˜50%) and selectivity (> 95%). After 20 h of reaction, PtSn/A750 showed a slight decrease in activity (39.9%) while the activity of PtSn/P200 dropped significantly (28.4%). Spent catalysts showed different metal sintering behavior and coke deposition which are well known causes for catalyst deactivation. A high strength of Lewis acid sites in A750 (higher Td in ethanol TPD) prevented the sintering of metal by strong metal-support interaction. Also, the lower number of Lewis acid sites in A750 than that of P200 reduced deposited coke on the catalysts (PtSn/A750: 1.8 wt% and PtSn/P200: 8.6 wt%). Furthermore, diffuse reflectance infrared Fourier-transform spectroscopy after CO adsorption at -150 °C clearly demonstrated that coke deposition was initiated from Lewis acid sites on the alumina surface, but then aromatization occurs at these sites. These results suggested that strong metal-support interactions to hold metal particles and less residual Lewis acid sites after metal loading to reduce coke deposition are important factors for designing stable and coke-resistant PtSn on alumina catalysts. Furthermore, precise characterization and understanding of the acid-base properties of alumina will contribute in developing catalysts with high stability.

Formation of porous α-alumina from ammonium aluminum carbonate hydroxide whiskers

Ammonium aluminum carbonate hydroxide (AACH) whiskers prepared by hydrothermal technique were employed as precursor material for development of porous alumina. After compaction of AACH whiskers at 8 bars, calcination was performed at 650 °C followed by sintering at different temperatures. The sintered samples were characterized by XRD, FTIR, SEM and mercury intrusion porosimetry. Mechanical strength was determined by compression testing. At sintering temperatures of 1200 °C to 1400 °C, the % age porosity was around 80%. At 1500 °C, the percentage porosity decreased to 71%. The as-prepared AACH consisted of bundles of whiskers with diameters as thick as 0.7 µm, while an individual whisker had a diameter of about 100 nm with an aspect ratio of about 33. A two-phase mixture consisting of θ- and α-alumina was obtained at 1100 °C, while at 1200 °C and above, single phase α-alumina was formed. θ-alumina retained the bundle-like morphology. However, transformation to α-alumina was accompanied by formation of bead-like morphology. These beads were joined together through necks/stems within the whiskers as well as across the parallel-lying whiskers. These necks grew at 1300 °C to form aggregates with smooth surfaces. At 1400 °C, these aggregates started joining with each other by neck formation and at 1500 °C, a three-dimensional network was formed. For sintering temperatures of up to 1400 °C, pores with sizes around 260 nm were very stable. At 1500 °C, significant pore growth took place along with an overall densification. Therefore, number of pores with sizes of around 260 nm decreased and those with sizes around 10 µm, 1 µm and 5 nm increased. The compression strength of samples sintered at 1100 °C to 1300 °C was in the range of 3.4–4.3 MPa. At 1400 °C, the strength increased to 5.2 MPa, while at 1500 °C, it jumped to 10.8 MPa due to the formation of three-dimensional network.

Seed-assisted hydrothermally synthesized AACH as the alumina precursors

Ammonium Aluminum Carbonate Hydroxide (AACH) is one of the nanostructure materials with a high surface area, which is mostly produced by the hydrothermal method. In this study, kinetics of the hydrothermal reaction has been accelerated with the addition of seed. Nucleation and growth steps have been studied by characterizing the obtained precipitate at different reaction times by FTIR, XRD, FE-SEM, and BET. Different amounts of seeds were added, and the optimum amount in reducing AACH crystallization time has been determined. By seed addition the time required for AACH formation has been reduced from 24h to around 10h, also the specific surface area of the AACH whiskers have been increased about 2.8 times. Mechanism of the reaction and the effect of seed addition have been discussed. Synthesized AACH was calcined at different temperatures to obtain different phases of alumina fibers. The surface area of the obtained Aluminas was investigated by BET; results showed that the highest surface area is achieved when the alumina is in the form of gamma structure.

Modification of polypropylene with nanosized α-Al2O3 powders prepared by the mechanochemical method

Nanosized [Formula: see text]-Al2O3 powders were prepared by the mechanochemical method, with AlCl[Formula: see text]H2O and NH4HCO3 as raw materials, the environmentally friendly starch as an effective dispersant. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to characterize the ammonium aluminum carbonate hydroxide (AACH) precursor and products. The results show that nanosized spherical [Formula: see text]-Al2O3 powders without hard agglomeration and with particle size in the range of 20–40 nm can be obtained by this novel and green method. Then, polypropylene (PP)/nano [Formula: see text]-Al2O3 nanocomposites were prepared by melt blending in a mixer apparatus. The crystallization behavior and mechanical properties of PP/[Formula: see text]-Al2O3 nanocomposites were further investigated in this study. Wide-angle X-ray diffraction (WAXD) results show that a small amount of [Formula: see text]-crystal of PP forms after adding [Formula: see text]-Al2O3 nanoparticles. According to differential scanning calorimetric (DSC) measurement, the [Formula: see text]-Al2O3 nanoparticles make crystallization temperature of PP enhanced by acting as effective nucleating agents. The tensile strength and impact strength were both improved significantly with the addition of [Formula: see text]-Al2O3 nanoparticles through tensile and impact tests. Scanning electron microscopy (SEM) observation showed that the fracture surface became rougher and further confirmed the above result.

Controllable preparation of γ-alumina nanoparticles with bimodal pore size distribution in membrane dispersion microreactor

In this paper, we present a new method for preparing γ-alumina nanoparticles with a bimodal pore size distribution by using an efficiently mixing membrane dispersion microreactor. NH4HCO3 and Al2(SO4)3∙18H2O were reacted under vigorous mixing to give an ammonium aluminum carbonate hydroxide (AACH) precursor. γ-Alumina was obtained by calcination of AACH at 550°C for 6h. The effects of NH4HCO3 concentration, pH during aging, and reaction temperature were investigated. The mechanism of bimodal pore formation was clarified. The results showed that large pores (10–100nm) were mainly formed in the reactor and during aging, and small pores (0–10nm) were mainly formed during calcination. When the concentration of NH4HCO3 was 1.5mol/L, the aging pH was 9.2, and the reaction temperature was 80°C, γ-alumina with a specific surface area of 504.7m2/g and pore volume of 1.76mL/g was obtained. The average size of the large pores was about 30nm, and the average size of the small pores was about 4nm.

Fabrication of hierarchical bristle-grass-like NH4Al(OH)2CO3@Ni(OH)2 core-shell structure and its enhanced Congo red adsorption performance

Hierarchical bristle-grass-like NH4Al(OH)2CO3@Ni(OH)2 core-shell structure is fabricated through a simple hydrothermal approach combined with subsequent chemical bath deposition. Electron microscopy characterization reveals that the ammonium aluminum carbonate hydroxide (NH4Al(OH)2CO3) microfibers were uniformly covered with interconnected and vertically aligned nickel(II) hydroxide (Ni(OH)2) nanosheets, forming hierarchical pore structure. The NH4Al(OH)2CO3 microfibers not only serve as substrate for the growth of the Ni(OH)2 nanosheets but also prevent the nanosheets from aggregating. The synthesized hierarchical bristle-grass-like NH4Al(OH)2CO3@Ni(OH)2 composite showed excellent adsorption performance toward Congo red (CR), which was superior to the aggregated Ni(OH)2 microspheres and the bare NH4Al(OH)2CO3 microfibers. The adsorption isotherm can be well described by the Langmuir model, with an estimated maximum adsorption capacity of 426 mg g−1 for the NH4Al(OH)2CO3@Ni(OH)2 composite. The major adsorption mechanism is electrostatic interaction between the CR molecules with negative charge and the positively charged sample surface of the Ni(OH)2 nanosheets at neutral pH. The as-prepared NH4Al(OH)2CO3@Ni(OH)2 core-shell microfibers can be expected to act as potential materials for CR removal in purification of wastewater.

Effects of chlorides on the phase transformation of alumina

The discovery that γ-alumina can be prepared at lower calcination temperature from an ammonium aluminum carbonate hydroxide (AACH) precursor templated with rosinyl trimethyl ammonium chloride has led to the assumption that Cl- is capable of lowering the temperature of the phase transformation of AACH to γ-alumina. To verify this hypothesis, several chlorides were introduced into the calcination process of the AACH precursor. The samples were characterized using X-ray diffraction, thermogravimetry and differential scanning calorimetry as well as X-ray photoelectron spectroscopy. The results showed that Cl- has great effects on the crystallinity of γ-alumina obtained by the calcination of AACH. The effects varied with the type, dosage and introduction method of the particular chloride. It was also found that Cl- began to take effect only after the AACH had been decomposed to form amorphous alumina. Therefore, the true function of Cl- is to decrease the temperature of the phase transformation from the amorphous phase to γ-alumina: the phase transformation temperature decreases by as much as 115 K.

Green synthesis of nanocrystalline α-Al2O3powders by both wet-chemical and mechanochemical methods

Nanosized [Formula: see text]-Al2O3powders were prepared with AlCl[Formula: see text]6H2O and NH4HCO3as raw materials by both wet-chemical and mechanochemical methods, through the synthesis of the ammonium aluminum carbonate hydroxide (AACH) precursor followed by calcination. The environmentally benign starch was used as an effective dispersant during the preparation of nanocrystalline [Formula: see text]-Al2O3powders. X-ray diffraction (XRD), thermogravimetric differential thermal analysis (TG-DTA), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to characterize the precursor AACH and products. The results show that nanosized spherical [Formula: see text]-Al2O3powders without hard agglomeration and with particle size in the range of 20–40 nm can be obtained by the two methods. Comparing the two “green” processes, the mechanochemical method has better prospects for commercial production.

Urea controlled hydrothermal synthesis of ammonium aluminum carbonate hydroxide rods

In this study, ammonium aluminum carbonate hydroxide (AACH) rods were controllably prepared using the hydrothermal method by manipulating the amount of urea in the reaction system. The experimental results showed that AACH in rod shape was able to be gradually transformed from γ-AlOOH in cluster shape during the molar ratios of urea to Al in the reactants were ranged from 8 to 10, and the yield of AACH has increased accordingly. When the molar ratio of urea to Al reaches 11, pure AACH rods with a diameter of 500 nm and a length of 10 μm approximately was able to be produced. Due to the slow decomposition of urea during the hydrothermal reaction, the nucleation and growth of AACH crystal proceed step by step. Therefore, the crystal can fully grow on each crystal plane and eventually produce a highly crystalline rod-shaped product. The role of urea in controlling the morphology and yield of AACH was also discussed in this paper systematically.

Morphology controlled Co-precipitation method for nano structured transparent MgAl2O4

Abstract MgAl2O4 spinel nano powders with various morphologies were synthesized with ammonium aluminum carbonate hydroxide by carbonate precipitation. The powders with rod, corn, and spherical morphologies were synthesized, varying the concentration of ammonium ions, by growth and aggregation of nano precipitates. The powders with spherical morphology formed spinel phase at a lower calcination temperature than those with other shapes. The morphology provided a superb sinterability due to improved particle packing. Although the synthetic conditions resulted in a composition slightly off the stoichiometric composition with Mg loss, this provided a proper condition for inhibiting grain growth. Finally, Mg-spinel which was obtained from spherical particles and fabricated by spark plasma sintering (SPS) showed much improved transparency with an average grain size of ~200 nm (RIT and TFT are 55.92% and 63.75% at 550 nm 75.35% and 78.91% at 1500 nm, respectively) than those from other shaped particles.

Ammonium aluminium carbonate hydroxide NH4Al(OH)2CO3 as an alternative route for alumina preparation: Comparison with the classical boehmite precursor

Ammonium aluminium carbonate hydroxide (AACH) is a promising alternative precursor for preparation of alumina with high purity and original textural properties. In this paper, both boehmite (classical alumina precursor) and AACH were precipitated in a stirred tank reactor with close process parameters. Preparation protocols were thus compared. Main differences between both protocols were pointed out (reactant molar ratio influence, alumina concentration, filtration/washing step). This study helps for the choice of the appropriate preparation route for alumina precursor synthesis. As-synthesized boehmite and AACH precursors were then calcined between 500°C and 1000°C. The textural properties of the corresponding aluminas were characterized. At 500°C, AACH-derived alumina revealed to be particularly porous, with larger mean pore diameter (ca. 29nm) than boehmite-derived alumina (ca. 6nm). Moreover, AACH-derived alumina exhibited a high surface area. However, a more accurate analysis revealed that this high specific surface area (407m2·g−1) is mostly due to microporosity formation during the calcination step. At higher calcination temperature, boehmite and AACH-derived aluminas exhibited different behaviors against sintering. In particular, the latter showed an interesting ability to maintain a constant mean pore diameter, regardless of the calcination temperature.

Facile synthesis of highly thermal-stable doped alumina with high surface area by low temperature solid-state reaction

Alumina and M-(La, Ba, Si) doped alumina were prepared by a facile low temperature solid-state reaction route and using cheap inorganic raw materials without any surfactants, in which only a harmless byproduct to environment was NH4Cl. The results show that all the prepared samples have a mesoporous structure and the BET surface area of as-synthesized alumina precursor has reached 326m2/g. Si-doped alumina exhibits remarkable thermal stability and high surface area (135–163m2/g) and the Ba-doped alumina have a large pore volume (0.44–0.95cm3/g) even after calcination at 1100°C for 10h. The nature of dopants and their concentrations have a significant influence on the textural properties and morphologies of M-alumina. The precursor synthesized can be converted to lower crystal ammonium aluminum carbonate hydroxide (AACH) by further thermal treatment. Si-doped alumina prepared by alumina from thermal decomposition of AACH possessed the superior thermal stability, and the surface area of 25%Si-Al2O3 calcined at 1100°C for 10h can reach 176m2/g. This facile synthetic route of alumina is an environmental friendly and convenient, and can be used in synthesis of other metal oxide porous materials.

Temperature sensitive synthesis of γ-Al2O3support with different morphologies for CoMo/γ-Al2O3catalysts for hydrodesulfurization of thiophene and 4,6-dimethyldibenzothiophene

Two different kinds of γ-Al2O3precursors: stick-like ammonium aluminum carbonate hydroxide and willow leaf-like boehmite could be selectively synthesizedviaa facile hydrothermal method by just adjusting reaction temperature.

Synthesis of high-surface-area rod-like alumina materials with enhanced Cr(VI) removal efficiency

A facile synthesis of rod-like alumina materials was developed through systematical investigation, which enables the control of the specific surface area of ammonium aluminium carbonate hydroxide (AACH) using aluminum nitrate as a precursor and urea as a precipitant. Our studies indicated that the molar ratio of CO(NH2)2/Al influences crystallinity, morphology and the surface area of alumina materials. Amorphous alumina materials with nanorod morphology and high surface area (1029 m2 g-1) was obtained with 15:1 M ratio of CO(NH2)2 to Al. In addition, the results demonstrated that thermal behaviors of the as-prepared AACH affect their crystallinities. Furthermore, the amorphous Al2O3 prepared from AACH by calcination at 773 K was used as an adsorbent for Cr(VI) removal from water solution, and external factors were investigated, including contact time, adsorbent dosage, initial concentration of adsorbate and the pH of solution. It was found that the maximum adsorption capacity of prepared amorphous Al2O3 for Cr(VI) was 52.1 mg g−1, which was higher than those of other reported Al2O3 samples.

Terahertz time domain spectroscopy of hydrothermally synthesized boehmite and ammonium dawsonite nanostructures

The frequency dependent optical and dielectric properties of boehmite (AlOOH) and ammonium aluminum carbonate hydroxide (AACH) nanostructures, prepared at different temperatures via hydrothermal synthesis, were studied by using terahertz time domain spectroscopy (THz-TDS). The complex refractive indices, absorption coefficients and complex dielectric constants were determined and compared for different synthesis temperatures. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) were also performed to confirm the formation of boehmite and AACH. Scanning electron microscopy (SEM) was performed to study the morphology of nanostructures. The study reveals the formation of AACH at higher temperatures and decrease in refractive index with increasing synthesis temperature. The higher absorption coefficient and lower refractive index and dielectric constant were observed for AACH than for boehmite.

In-situ Cr-doped Alumina Nanorods Powder Prepared by Hydrothermal Method

Cr-doped ammonium aluminum carbonate hydroxide nanorods were prepared by a hydrothermal method, with Al(NO3)3·9H2O, Cr(NO3)3·9H2O, and urea as raw materials and PEG-20000 as surfactant. In-situ Cr-doped alumina nanorods powder was obtained through calcining its precursors (Cr-doped ammonium carbonate hydroxide nanorods) at 1200 °C. The crystal composition, the structure and the morphology of the as-prepared products were characterized by XRD, SEM and FTIR. Besides, the color performances of the products were analyzed by UV/Vis/NIR spectrometer and automatic color measurement. Results show that the precursors of Cr-doped alumina nanorods powder prepared by the hydrothermal method are composed of uniform nanorods. After its calcinations at 1200 °C, the in-situ doping of Cr in the alumina substrate is achieved. In the Cr-doped alumina nanorods powder, a continuous solid solution of Cr2O3 and Al2O3 is formed, which has a corundum crystal structure. With the increasing Cr content, Cr-doped ammonium aluminum carbonate hydroxide nanorods gradually become short, and the melting phenomenon occurs in calcined products. UV-Vis spectroscopy analysis shows that Cr-doped alumina nanorods powder has three strong absorption bands at 562, 406 and 372 nm, thus leading to a pink color for samples which is in agreement with chromatic data. In the present study, Cr-doped alumina nanorods powder prepared by the hydrothermal method can reduce the formation temperature of corundum crystal structures and resolve the problem of mixing homogeneity of Al2O3 and Cr2O3, which will contribute to the preparation and the application of alumina-chrome refractory, pink corundum abrasive and ceramic pigment.

Influence of Al2O3 whisker concentration on mechanical properties of WC–Al2O3 whisker composite

A novel WC–Al2O3 whiskers composite was prepared with the addition of VC grain growth inhibitor by hot-pressing sintering. The aim of this investigation was to study the influence of varying whisker concentration (2.5, 5, 10 and 15wt%) on mechanical properties of WC–Al2O3 whisker composite. Whiskers of hydrothermally synthesized Ammonium Aluminum Carbonate Hydroxide (AACH) were used for composite synthesis. These whiskers transformed in situ into alumina and keep their morphology even after sintering. Results demonstrated that the hardness were decreased slightly with the increasing content of Al2O3 whiskers, the fracture toughness and flexural strength reached to maximum value of 13.8MPam1/2 and 1335±42MPa respectively, when the concentration of Al2O3 whiskers is 10wt%. Compared to those composites reinforced by 10wt%Al2O3 particle, the values of flexural strength increased by roughly 10wt%. The strengthening mechanisms were attributed to crack deflection, crack bridging and ligamentary bridging between crack surfaces. When the concentration of whiskers goes beyond 10wt%, the agglomerates created low density regions and resulted in lowering of strength.

Large-scale synthesis of aluminium borate nanowires by a simple molten salt method

Aluminum borate nanowires were synthesized in a molten salt method at 1100°C in the air by using ammonium aluminum carbonate hydroxide (AACH) and H3BO3 as starting materials. The as-synthesized samples were examined by XRD and SEM. The results showed that Al18B4O33 nanowires with an orthorhombic structure were formed at 1100°C. A self-catalytic mechanism was proposed for the growth mechanism of the nanowires on the basis of the experimental phenomena.

Hydrodesulfurization of 4,6-Dimethyldibenzothiophene over CoMo Catalysts Supported on γ-Alumina with Different Morphology

Nanostructured γ-alumina with two different morphologies (rod-like and cube-like) was used as support for CoMo hydrodesulfurization catalyst. Both γ-aluminas were prepared by thermal decomposition of ammonium aluminum carbonate hydroxide precursor, which was synthesized by a convenient hydrothermal method at two pH values. Fourier transform infrared spectroscopy of prydine adsorption, thermogravimetric analysis, and 27Al magic angle spinning (MAS) NMR showed that the rod-like γ-alumina exhibited a lower acidity than the cube-like γ-alumina. The result of X-ray diffraction and temperature-programmed reduction indicated that CoMo oxidic catalysts supported on the rod-like γ-alumina presented higher reducibility compared to those of cube-like γ-alumina, because more β-CoMoO4 was formed on the surface of the rod-like γ-alumina than that of the cube-like γ-alumina. After sulfidation, a large stack with slightly longer MoS2 slabs was formed on the rod-like γ-alumina supports, thereby creating a catalyst with hi...

A Decomposition Route for Synthesis of Al2O3 Crystal and its Applications as Thermal Conductivity Filler

Platelike α‐Al2O3 powder was obtained at 850°C by thermal decomposition of ammonium aluminum carbonate hydroxide precursor, which was treated by hydrofluoric acid. The results showed the decomposition of the as‐prepared precursors experienced via three steps, adsorption of physical water, dehydration of crystalline water, and decomposition of the precursor, and the activation energies of the above three steps were calculated using the Coats–Redfern method. Meanwhile, the intermediate of (NH4)3AlF6 obtained played an important role in decreasing activation energy of the decomposition and phase transformation. Moreover, the thermal conductivity of the epoxy resin filled with platelike alumina was improved obviously.