γ-Al2O3 Materials Research Articles

Evaluation of the Adsorptive Performance of Rambutan-shaped γ-Al2O3 Micro-nanostructure against Wastewater Containing the Azo Dye: Methyl Orange

Aim: The aim of this study is to explore and evaluate the possibility of rambutan-shaped micro-nanostructured γ-Al2O3 material’s usage as an adsorbent in industrial wastewater processing. Background: Every year, more than 7 million tons of dyestuff-containing wastewater are produced in the industry. Although there are many adsorbents like fly ash and clays, the shortages limit their actual applications. It is still necessary to find a new cheaper adsorbent. Objective: The paper aimed to investigate the adsorption capacity and decolorization ability of rambutan- shaped γ-Al2O3 material synthesized via a composite soft template method. Methods: The rambutan-shaped γ-Al2O3 material was prepared and characterized via XRD, TEM, FE-SEM, and FT-IR (See our group’s published article in “Ming Shen*, et al., Acta Phys.-Chim. Sin. 2013, 29 (10), 2286-2294”). The methyl orange aqueous solution was selected as the model of industrial wastewater. The methyl orange solution (15.0 mg·L-1) with different pH (2~9) was exposed to a series of amounts of γ-Al2O3 powder ranging from 10.0 to 70.0 mg. Different concentrations of methyl orange solution, ranging from 5.0 to 200.0 mg·L-1 were also tested with the same amount of γ-Al2O3 powder (50.0 mg). The adsorption-calcination cycle analysis was performed with methyl orange solution (50.0 mg·L-1) and 500.0 mg of γ-Al2O3 powder at pH=3. Results: The γ-Al2O3 material exhibits excellent adsorption capacity (114.10 mg·g-1) towards acidic methyl orange aqueous solution. At the same time, the decolorization rate of the γ-Al2O3 material reaches about 88%. This material still keeps a 50% decolorization rate after 6 repeats of the adsorption- calcination cycle. Moreover, the excellent self-sedimentation ability of this material also provides an easy separation for future industrial applications. Conclusion: The γ-Al2O3 material with rambutan-like micro-nanostructure presents excellent adsorption capacity/decolorization ability and self-sedimentation ability. It can be used as a new type of adsorbent for wastewater processing. The rambutan-shaped micro-nanostructure plays an important role in maintaining the adsorption ability of the γ-Al2O3 material.

SYNTHESIS AND CHARACTERIZATION OF γ-Al2O3@MgO SORBENT FOR EFFICIENT Pb REMOVAL FROM AQUEOUS SOLUTIONS

This study focuses on enhancing the adsorption capacity for lead ions by introducing MgO onto the surface of γ-Al2O3, forming γ-Al2O3@MgO. The γ-Al2O3 nanoparticles were synthesized via the sol-gel method on a citrate template. MgO was incorporated onto the surface of the γ-Al2O3 nanoparticles, with varying MgO concentrations (5%, 10%, and 15% by weight), achieved through the absorption of magnesium ions onto the material's surface followed by sintering at 773K. The findings indicated that both the γ-Al2O3 and MgO crystalline phases exhibit a cubic structure (Fd3m symmetry group), which is formed within the sample. Although the specific surface area diminished from 166 m2/g to 135 m2/g, the surface basicity increased proportionally to the amount of MgO incorporated into the sample. The impacts of various absorption conditions such as pH, adsorbent mass, and contact time on the Pb2+ ion adsorption capacity was systematically examined. Optimal conditions (pH=7, adsorption time of 8 hours) highlighted that the γ-Al2O3 material containing 10% MgO by weight showcased the highest Pb2+ adsorption capacity at 145 mg/g, surpassing the adsorption capacity of 135 mg/g for the γ-Al2O3 material.

Experimental gas-fluidized bed drying study on the segregation and mixing dynamics for binary and ternary solids

Fluidized bed drying is an evolving process: The bed hydrodynamics, including the segregation and mixing tendencies, and its interplay with mass and heat transfer change in time. In this study, pseudo-2D fluidized bed experiments are performed using binary (50/50%) and ternary (33.3/33.3/33.3%) solids mixtures. A coupled particle image velocimetry infrared thermography technique provides local solids velocity and temperature fields. Furthermore, a machine learning algorithm is applied to characterize the bed segregation and mixing dynamics. Significant hydrodynamic changes and various segregation and mixing tendencies due to the evaporation of water from the porous γ-Al2O3 material were observed. A competition between size and density-based segregation and mixing dynamics resulted in changing bed configurations, which are correlated to the local solids drying behavior. Besides, it showed that drying of wider size distributions could lead to more complex efficient process operation.

Europium-Magnesium-Aluminum-Based Mixed-Metal Oxides as Highly Active Methane Oxychlorination Catalysts.

Methane oxychlorination (MOC) is a promising reaction for the production of liquefied methane derivatives. Even though catalyst design is still in its early stages, the general trend is that benchmark catalyst materials have a redox-active site, with, e.g., Cu2+, Ce4+, and Pd2+ as prominent showcase examples. However, with the identification of nonreducible LaOCl moiety as an active center for MOC, it was demonstrated that a redox-active couple is not a requirement to establish a high activity. In this work, we show that Mg2+-Al3+-based mixed-metal oxide (MMO) materials are highly active and stable MOC catalysts. The synergistic interaction between Mg2+ and Al3+ could be exploited due to the fact that a homogeneous distribution of the chemical elements was achieved. This interaction was found to be crucial for the unexpectedly high MOC activity, as reference MgO and γ-Al2O3 materials did not show any significant activity. Operando Raman spectroscopy revealed that Mg2+ acted as a chlorine buffer and subsequently as a chlorinating agent for Al3+, which was the active metal center in the methane activation step. The addition of the redox-active Eu3+ to the nonreducible Mg2+-Al3+ MMO catalyst enabled further tuning of the catalytic performance and made the EuMg3Al MMO catalyst one of the most active MOC catalyst materials reported so far. Combined operando Raman/luminescence spectroscopy revealed that the chlorination behavior of Mg2+ and Eu3+ was correlated, suggesting that Mg2+ also acted as a chlorinating agent for Eu3+. These results indicate that both redox activity and synergistic effects between Eu, Mg, and Al are required to obtain high catalytic performance. The importance of elemental synergy and redox properties is expected to be translatable to the oxychlorination of other hydrocarbons, such as light alkanes, due to large similarities in catalytic chemistry.

Catalytic decomposition sensing mechanism of mesoporous gamma alumina for freon R134a detection

Freon R134a is a widely used refrigerant that can cause a severe greenhouse effect and should be detected on site. However, it is a big challenge for semiconductor gas sensors to detect the inert Freon R134a molecules. Herein, mesoporous γ-Al2O3 is synthesized and loaded on top of ZnO sensing materials to form a bilayer microsensor to realize high-performance detection of Freon R134a. The mesoporous γ-Al2O3 material first decomposes the inert R134a molecule into a large number of active radicals. The generated reactive radicals are then easily sensed by the ZnO material. The limit of detection (LOD) of the bilayer sensor reaches the ppm level, which meets the requirements for on-site detection of Freon R134a leakage. The online mass spectrum (online MS) is used to identify the produced radicals qualitatively. According to the online MS results, the catalytic mechanism of mesoporous γ-Al2O3 for Freon R134a molecules has been clearly revealed.

Experimental investigation of monodisperse solids drying in a gas-fluidized bed

Fluidized bed drying is an unsteady process where particle and gas properties evolve in time. The bed hydrodynamics and its interplay with mass and heat transfer changes in time. In this study, experiments in a pseudo-2D fluidized bed setup are performed to obtain insight in this complex behavior. A coupled particle image velocimetry infrared thermography technique provides solids velocity and temperature fields in the bed. Significant hydrodynamic changes due to the evaporation of water from the porous γ-Al2O3 material for three superficial velocities were observed. The 1.25 umf case resulted in an fixed bed state, but after drying for 580 s a bed inversion took place. The 1.50 and 1.75 umf experiments showed an increase in bed expansion over time. Furthermore, clear asymmetrical solids volume fluxes were observed for the wet material that became more symmetrical over time when the material dried.

Revisiting Edge Sites of γ-Al2O3 Using Needle-Shaped Nanocrystals and Recoupling-Time-Encoded {27Al}-1H D-HMQC NMR Spectroscopy

Despite being widely used in numerous catalytic applications, our understanding of reactive surface sites of high-surface-area γ-Al2O3 remains limited to date. Recent contributions have pointed toward the potential role of highly reactive edge sites contained in the high-field signal (−0.5 to 0 ppm) of the 1H NMR spectrum of γ-Al2O3 materials. This work combines the development of well-defined, needle-shaped γ-Al2O3 nanocrystals having a high relative fraction of edge sites with the use of state-of-the-art solid-state NMR to significantly deepen our understanding of this specific signal. We are able to resolve two hydroxyl sites with distinct isotropic chemical shifts of −0.2 and −0.4 ppm and different positions within the dipole–dipole network from 1H–1H single-quantum double-quantum NMR. Moreover, the use of recoupling-time-encoded arbitrary-indirect-dwell dipolar heteronuclear multiple quantum coherence allows us to partially revise previous assignments for surface-aluminum sites in the proximity of these hydroxyl sites. Although previous work has ascribed the high-field signal to be correlated with a single four-coordinate Al-site with a substantial quadrupolar broadening of >10 MHz, we can identify the presence of two four-coordinate Al-sites with similar isotropic chemical shifts but different quadrupolar coupling constants of approximately 7 and >10 MHz, respectively. Recoupling-time-encoded data are thus able to differentiate sites that would otherwise only be achievable with access to multiple fields or usage of highly advanced NMR techniques.

Precise tuning the CoMoOx/Al2O3 and CoMoSx/Al2O3 interfacial structures for efficient hydrodesulfurization of dibenzothiophene

In this work, we studied how the oxidic CoMoOx/Al2O3 and sulphurated CoMoSx/Al2O3 interfacial structures determine catalytic efficiency in selective hydrodesulfurization (HDS) of dibenzothiophene (DBT). To achieve this goal, we first synthesized the γ-Al2O3 materials of unique morphologies through the ionic liquid-assisted hydrothermal process under different conditions. The resulting γ-Al2O3 hexagonal plates (HP) and stacked hexagonal plates (SHP) are single crystallites with the dominant (110) and (111)/(100) facet structures, respectively; whereas the Al2O3 rods show polycrystalline feature. Through impregnation of Mo/Co salts of different loadings, the various CoMoOx precursors were generated on the different Al2O3 facets owing to the distinct interaction: mostly the two-dimensional (2D) poly-/mono-meric MoOx species together with the three-dimensional (3D) MoO3 on the Al2O3 (110) facet vs. the quasi 2D polymeric MoOx species on the Al2O3 polycrystalline facet. Such structural difference further affected the sulfidation of the MoCoOx as well as the quantity of active MoCoSx entities on different γ-Al2O3 supports: 10Mo3CoSx/Al2O3-HP had the highest level of MoCoOx sulfidation thus a much higher fraction of MoS2 plus Co9S8/CoMoS species whereas less quantity of partially sulphurated CoMoOxS2/CoOx together with SOx2-species. All the distinct interfacial domains of the sulphurated catalysts reasonably account for significantly different efficiency in HDS of DBT. Surface MoS2/CoMoS/Co9S8 species of the highest content over the Al2O3 (110) facet correspond to the highest DBT areal conversion rate and TOF value, owing to the enhanced MoS2-Co9S8 and MoS2-CoMoS conjunction and synergism.

Effect of different supports on activity of Mn–Ce binary oxides catalysts for toluene combustion

The effects of support materials on catalytic performance were investigated in catalytic removal of toluene. And the Mn–Ce binary oxides as active components were supported on ZrO2, SiO2, γ-Al2O3 and TiO2 support materials. Many techniques, including X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR) and NH3-temperature-programmed desorption (NH3-TPD), were used to characterize physicochemical properties. Among the different catalysts, the MnCe/ZrO2 catalyst with the lowest specific surface area (39.7 m2/g) shows the best catalytic activity. In terms of toluene conversion, the activity order is as follows: MnCe/ZrO2 > MnCe/TiO2 ≈ MnCe/SiO2 > MnCe/Al2O3. The better performance of MnCe/ZrO2 should be attributed to the low-temperature reducibility, and abundant surface species (Mn4+ and lattice oxygen). And XPS and TPR results reveal that more surface abundant Mn and Ce elements generate good interaction in MnCe/ZrO2. The weak interaction between metal oxide and support also boosts the dispersion and complete reduction of MnCe oxides at low temperature. In addition, the in-situ DRIFTS results clarify that the carbonate species are main intermediates in MnCe/ZrO2 sample during surface reaction process.

Enhancement of HDO Activity of MoP/SiO2 Catalyst in Physical Mixture with Alumina or Zeolites

Catalytic properties of physical mixture of MoP/SiO2 catalyst with SiC, γ-Al2O3, SAPO-11 and zeolite β have been compared in hydrodeoxygenation of methyl palmitate (MP). MoP/SiO2 catalyst (11.5 wt% of Mo, Mo/P = 1) was synthesized using TPR method and characterized with N2 physisorption, elemental analysis, H2-TPR, XRD and TEM. Trickle-bed reactor was used for catalytic properties investigation at hydrogen pressure of 3 MPa, and 290 °C. The conversions of MP and overall oxygen-containing compounds have been increased significantly (from 59 to about 100%) when γ-Al2O3 or zeolite materials were used instead of inert SiC. MP can be converted to palmitic acid through acid-catalyzed hydrolysis along with metal-catalyzed hydrogenolysis, and as a consequence the addition of material possessing acid sites to MoP/SiO2 catalyst could lead to acceleration of MP hydrodeoxygenation through acid-catalyzed reactions. Isomerization and cracking of alkane were observed over the physical mixture of MoP/SiO2 with zeolites, but the selectivity of MP conversion trough the HDO reaction route is remained on the high level exceeding 90%.

SHS Membrane for the Dehydrogenation of n-Butanol to Butadienes

We have synthesized catalytically active membranes based on α- and γ-Al2O3 powders for the dehydration and dehydrogenation of butyl alcohol to butadiene and hydrogen. The open porosity of the samples obtained in this study is 41% in the case of α-Al2O3 and 38% in the case of γ-Al2O3. The open pore size is 4.6–5.1 μm in the α-Al2O3 material and 0.5–0.8 μm in the γ-Al2O3 material. We have implemented a hybrid, membrane–catalytic process for the dehydrogenation of butanol by combining reaction and hydrogen separation steps in a single device. It has been demonstrated that the dehydration of n-butanol on a γ-Al2O3 converter leads to the formation of a butylene fraction with a selectivity of 99.88–100% at a temperature of 300°C, which is 50°C lower than in the case of commercially available gamma-alumina granules. The dehydrogenation of butylene to butadiene on an α-Al2O3 membrane with selective hydrogen removal from the reaction zone has made it possible to raise the 1,3-butadiene output from 16.5 to 22.6 L/(h gact. comp.), with the degree of ultrapure hydrogen extraction reaching ~16%. After the experiment was run for 20 h, no decrease in the catalytic activity of the system was detected, as distinct from commercial solutions, in which a regeneration step is necessary every 8–15 min.

Synthesis of mesoporous γ-Al2O3 by using cellulose nanofiber as template for hydrodesulfurization of dibenzothiophene

Mesoporous γ-Al2O3 materials with different channel properties were successfully synthesised by using cellulose nanofiber (CNF) as template. The corresponding NiMo catalysts were prepared and further evaluated in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). The as-synthesised γ-Al2O3 supports and NiMo catalysts were characterized by XRD, nitrogen adsorption-desorption, H2-TPR, Raman, SEM, TEM, XPS and HRTEM techniques. The NiMo/MA-7 catalyst displayed the highest DBT conversion at all liquid hourly space velocities (LHSVs). At high LHSV of 150 h−1, DBT HDS efficiency over NiMo/MA-7 (∼30%) is about six times than that of the comparison catalyst NiMo/MA-0 (5%) without CNF addition. This outstanding performance attributed to synergistic effects of open mesoporous structure, appropriate dispersion and stacking morphology of active metals, and the suitable MSI (metal-support-interaction). In addition, the products distributions of all catalysts in the HDS of DBT were investigated, and it is found that HYD/DDS ratio was promoted after using CNF as template agent.

Catalytic dehydration of ethanol-to-ethylene over Rho zeolite under mild reaction conditions

Abstract A small-pore zeolite, Rho having 8-membered ring opening and 3-dimensional (3-D) channels is synthesized via a greener process, without the use of a structure-directing agent. The zeolite Rho is crystallized by a conventional hydrothermal reaction under static conditions. XRD pattern showed phase purity of RHO-type crystalline topology, and SEM images depicted polyhedral particles with bimodal size distribution. The average size of small and large sized particles are 200 nm and 1000 nm, respectively. The amount of total solid-acid sites on Rho zeolite is 2.534 mmol g−1 and BET specific surface area reached to 812 m2 g−1. The zeolite is tested for a gas-phase conversion of ethanol-to-ethylene in the temperature range of 200–400 °C. The catalytic efficiency and stability of Rho zeolite are compared with the materials extensively used in the dehydration of alcohols; a control zeolite (ZSM-5) and three different samples of γ-Al2O3. For ethanol dehydration under mild reaction conditions, the overall catalytic efficiency of Rho is superior to that of the ZSM-5 zeolite and the γ-Al2O3 materials. The strength and concentration of solid-acid sites are the main driving factors in the low-temperature dehydration of ethanol-to-ethylene.

Influence of the support of copper catalysts on activity and 1,2-dichloroethane selectivity in ethylene oxychlorination

Five different support materials were modified with 5 wt.% Cu, using an evaporation impregnation method. The synthesized CuCl2/γ-Al2O3, CuCl2/TiO2 (Hombikat), CuCl2/TiO2 (Alfa Aesar), CuCl2/SiO2 and CuCl2/H-Beta-25 materials were characterized by nitrogen physisorption, X-ray powder diffraction, scanning electron microscopy, energy dispersive Xray microanalysis, transmission electron microscopy, Fourier transform infrared spectroscopy and CO2-temperature programmed desorption. The physical-chemical characterization was correlated with catalytic activity, stability and selectivity in the ethylene oxychlorination. It was found that γ-Al2O3 and TiO2 support materials demonstrate very good activity and 1,2dichloroethane selectivity compare to other catalysts. Zeolite H-Beta-25 and SiO2 support materials proved to be unusable for this reaction.

High Yield Manufacturing of γ-Al2O3 Nanorods

This paper presents a high aluminum yield route for the large-scale production of nanostructured alumina with high morphological purity. Morphologically selective hydrothermal formation of alumina nanorods can be achieved at low pH values ( 95 wt % aluminum yield. The γ-Al2O3 materials produced by the recycle procedure possess the same crystallinity, surface area and morphology as the γ-Al2O3 nanorods obtained from the batch hydrothermal route. We have explored the potential accumulation of spectator ions from recycling the supernatant and no effect on the ...

Synergetic Effect of Ni2P/SiO2 and γ-Al2O3 Physical Mixture in Hydrodeoxygenation of Methyl Palmitate

The Ni2P/SiO2 catalyst, which was prepared by in situ temperature-programmed reduction and in the mixture with the inert (SiC, SiO2) or acidic (γ-Al2O3) material was studied in methyl palmitate hydrodeoxygenation (HDO). Methyl palmitate HDO was carried out at temperatures of 270–330 °C, H2/feed volume ratio of 600 Nm3/m3, and H2 pressure of 3.0 MPa. Ni2P/SiO2 catalyst, diluted with γ-Al2O3 showed a higher activity than Ni2P/SiO2 catalyst diluted with SiC or SiO2. The conversion of methyl palmitate increased significantly in the presence of γ-Al2O3 most probably due to the acceleration of the acid-catalyzed reaction of ester hydrolysis. The synergism of Ni2P/SiO2 and γ-Al2O3 in methyl palmitate HDO can be explained by the cooperation of the metal sites of Ni2P/SiO2 and the acid sites of γ-Al2O3 in consecutive metal-catalyzed and acid-catalyzed reactions of HDO. The obtained results let us conclude that the balancing of metal and acid sites plays an important role in the development of the efficient catalyst for the HDO of fatty acid esters over supported phosphide catalysts.

Preconcentration and Separation of Cr(VI) Coupled with Controllable Synthesis of Nano γ-Al2O3 Materials

The γ-alumina nano materials were acquired through hydrothermal method of controllable synthesis. Optimized methods were used to change the hydrothermal parameters on the synthesis of nano γ-Al2O3. The preconcentration performance of chromium(VI) was explored comparing with SDS and CTMAB in the presence of precursors which were prepared via Al(NO3)3·9H2O and CO(NH2)2. 170 °C was selected as reaction temperature and SDS was chosen as surfactant. TEM images indicated that the average particle size of granular γ-Al2O3 was between 100 nm to 400 nm whose dispersion tended to be good. After centrifugation, a certain volume of 2 mol·L-1 hydrochloric acid was used as eluent. At the same time, chromium(VI) adsorbed in granular γ-Al2O3 aggregation was analyzed by inductively coupled plasma mass spectrometry. It was showed that the effect of branch type was not better than the granule type. The adsorption limit of Cr(VI) in γ-Al2O3 synthesized by SDS was higher than that of CTMAB. Further experiments of the interfering elements showed that Sb, As, total Cr, Se in granular γ-Al2O3 had higher adsorption rate, which could reach to 90% or more. When eight migrating elements shared some adsorption sites with Cr(VI), the adsorption rate and limitation reduced. The competitive adsorption effect of Ba, Cd, Pb and Hg had little impact on Cr(VI). As a result, this established method had reached the requirements of Cr(VI) combined with separation and detection in environmental sewage which could be used for analysis of other heavy metals.

Low-temperature methanol dehydration to dimethyl ether over various small-pore zeolites

Eight-membered ring small-pore zeolites Rho and KFI have been synthesized, characterized and tested for dehydration of methanol to dimethyl ether at low-temperature, and compared with other zeolites and three different samples of γ-Al2O3. Both the zeolites were mainly crystallized from the synthesis gels with the Si/Al ratio of 5.0 by a conventional hydrothermal method without any agitation. The amount of total solid-acid sites was 1.65mmolg−1 and 2.53mmolg−1 for zeolite KFI and Rho, respectively. In addition, zeolites SSZ-13, RUB-13, and ZSM-5 were also employed for the reaction. Reaction conditions were optimized for a low-temperature catalytic dehydration of methanol selectively to dimethyl ether. Methanol dehydration efficiency of various zeolitic frameworks is discussed against the strength of solid-acidity, type of channel structure, specific surface area, and particle size. At temperatures≤200°C, the overall catalytic efficiency of the small-pore zeolites with appropriate medium-strong acidity and 3-D channels was superior to that of the reference γ-Al2O3 materials.

Effect of synthesis temperature on structure-activity-relationship over NiMo/γ-Al2O3 catalysts for the hydrodesulfurization of DBT and 4,6-DMDBT

A series of γ-Al2O3 materials with different textural properties and acidities were synthesized from the boehmite sol by tuning the aging temperatures. NiMo supported catalysts were prepared by using γ-Al2O3 as the supports, then the catalytic HDS performance were evaluated by using DBT and 4,6-DMDBT to be the probe molecules. The physico-chemical properties of γ-Al2O3 supports and the corresponding NiMo catalysts were characterized by XRD, N2-physisorption, Py-IR, UV–Vis DRS, laser Raman spectra, H2-TPR, XPS, HRTEM methods. The characterization results showed that NiMo/γ-363 catalyst possessed a large pore size (12.0nm), open pore volume (0.86cm3g−1), moderate acidity and appropriate MSI. The NiMo/γ-363 catalyst presented the highest DBT and 4,6-DMDBT conversions at all the WHSVs. The NiMo/γ-363 catalyst showed highest kHDS and TOF values of the 4,6-DMDBT HDS, which could be ascribed to the synergistic effect of excellent textural properties, appropriate acidity and suitable MSI of the NiMo/γ-363 catalyst, moderate dispersion degree, high sulfidation degree and desirable stacking morphology of the MoS2 crystallites. The highest HYD/DDS ratio (1.51) of the 4,6-DMDBT HDS over the NiMo/γ-363 catalyst indicated that the HYD pathway was the main reaction route. Furthermore, a possible reaction network for 4,6-DMDBT HDS over the series of NiMo/γ-Al2O3 catalysts was proposed.

Performance Comparison of Spray-dried Mn-based Oxygen Carriers Prepared with γ-Al2O3, α-Al2O3, and MgAl2O4as Raw Support Materials

Performance Comparison of Spray-dried Mn-based Oxygen Carriers Prepared with γ-Al2O3, α-Al2O3, and MgAl2O4as Raw Support Materials