Porous γ-Al2O3 Research Articles

Alkali promoted tungsten carbide as a selective catalyst for the reverse water gas shift reaction

The conversion of CO2 to CO via the reverse water gas shift (RWGS) reaction is often envisioned as the first step in the large scale transformation of CO2 into value added hydrocarbons. Accordingly, low-cost and highly selective RWGS catalysts are desirable materials for sustainable CO2 utilization. Here, we describe synthesis, characterization and performance evaluation of alkali metal promoted tungsten carbide (WC) RWGS catalysts, supported on porous γ-Al2O3. Scanning electron microscopy reveals significant differences in the morphology of the catalysts, while X-ray photoelectron spectroscopy indicates a greater extent of carburization of the alkali-promoted catalysts, suggesting that alkali metals act as structural and electronic promoters, respectively. Performance data for the RWGS reaction at 300 and 350 °C shows all catalysts are active, with the alkali promoted catalysts demonstrating improved CO selectivity. Of the catalysts tested, the highest CO yield is achieved using K-promoted WC, demonstrating K-WC/γ-Al2O3 is a low-cost, active and selective RWGS catalyst.

Microwave-Assisted Hydrothermal Synthesis of [Al(OH)(1,4-NDC)] Membranes with Superior Separation Performances.

In this study, we report a facile ligand-assisted in situ hydrothermal approach for preparation of compact [Al(OH)(1,4-NDC)] (1,4-NDC=1,4-naphthalenedicarboxylate) MOF membranes on porous γ-Al2 O3 substrates, which also served as the Al3+ source of MOF membranes. Simultaneously, it was observed that the heating mode exerted significant influence on the final microstructure and separation performance of [Al(OH)(1,4-NDC)] membranes. Compared with the conventional hydrothermal method, the employment of microwave heating led to the formation of [Al(OH)(1,4-NDC)] membranes composed of closely packed nanorods with superior H2 /CH4 selectivity.

Macroporous Hydrogen Manganese Oxide/Al2O3 for Effective Lithium Recovery from Seawater: Effects of the Macropores vs Mesopores

Hydrogen manganese oxide (HMO) has been widely investigated for recovery of lithium (Li) from seawater. For a practical application, it is essential to obtain a granulated HMO. However, granulation of HMO interferes seawater diffusion, thereby decreasing the Li adsorption performance. To minimize the hindrance of Li adsorption performance, macroporous LMO/Al2O3(MLA) was synthesized in this study. Highly porous γ-Al2O3 results in plenty of mesopores in cylindrical LMO/Al2O3. In addition, macropore is induced in LMO/Al2O3 by addition of hydrogel beads. During calcination, the hydrogel beads decomposed, leaving spherical macropores (500–1000 μm). After delithiation, Li adsorption performance of MLAs was evaluated in Li-spiked seawater. At high Li concentrations, all MLAs exhibited similar Li adsorption capacities. However, at low Li concentration (<50 mg/L), only MLA with the highest macropore density (porosity ≈ 60.3%) showed Li uptakes similar to that of HMO powder. In a dilute Li solution, such as seawate...

Recycling of Secondary Aluminum Dross to Fabricate Porous &amp;lt;i&amp;gt;γ&amp;lt;/i&amp;gt;-Al&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; Assisted by Corn Straw as Biotemplate

In the aluminum industry, secondary aluminum dross (SAD) is an inevitable solid residue, which usually contains 30 - 70 wt% Al2O3. In this work, Al(OH)3 was extracted from SAD through acid-leaching and alkali purification process. The as-obtained Al(OH)3 precipitation then was calcinated to synthesize porous γ-Al2O3 assisting by an agricultural waste biomass-corn straw as biotemplate. Effects of H2SO4 concentration, reaction temperature and time on the recovery of SAD were investigated. Furthermore, the dependence of calcination temperature on specific surface area, pore volume and content of porous γ-Al2O3 was analyzed. X-ray diffraction (XRD) and X-ray fluorescence (XRF) were used to inspect the phase compositions and their contents, respectively. Scanning electron microscopy (SEM) was employed to analyze the morphologies of the sintered porous γ-Al2O3. It was found that the highest recycle rate of aluminum from SAD was obtained under optimum conditions of 80°C, acid concentration of 1.6 mol/l, and reaction time of 5 h by acid process. The porous γ-Al2O3 with specific surface area, 261.22 m2/g and average pore diameter, 52.64 nm, was obtained under calcination at 850°C through mixing the as-obtained Al(OH)3 precipitation and corn straw.

Preparation of solid acid catalyst SO42−/TiO2/γ-Al2O3 for esterification: A study on catalytic reaction mechanism and kinetics

Abstract In this work, a series of SO42−/TiO2/γ-Al2O3 solid acid catalysts were synthesized by impregnation method, in which nano-TiO2 was prepared by sol–gel method, and then the nano-TiO2 sol was loaded on porous γ-Al2O3 supporter through impregnation. The structure and property of catalyst were characterized by XRD, N2-BET, SEM, TEM, XPS, NH3-TPD, Pyridine-IR and FT-IR. In addition, the catalyst of chelate bidentate coordination acid center model was established. The catalytic performance test was carried out in the esterification of n-butyl alcohol with lauric acid and the catalyst showed excellent activity. The experimental results showed that the medium strength acid sites were more dominant active sites than the strong and weak acid sites for the rapid esterification reaction. Its kinetic behaviors and activation energy were studied for the esterification under the catalytic reaction condition.

In situ formation of a multiporous MOF(Al)@γ-AlOOH composite material: A versatile adsorbent for both N- and S-heterocyclic fuel contaminants with high selectivity

We report here for the first time an in situ green synthetic approach for the formation of a multiporous (mesoporous) composite, Al(OH)(1,4-NDC)@γ-AlOOH, via a direct hydrothermal reaction between 1,4-H2NDC (1,4-naphthalene dicarboxylic acid) and millimeter-sized porous γ-Al2O3 beads. This composite material has been well characterized using various analytical techniques. It has been used for the stationary solid phase adsorption of sulfur-containing (SCCs) and nitrogen-containing compounds (NCCs) from both a model oil and a real fluid cracking (FCC) oil. The adsorption capacities decreased in the order of benzothiophene > dibenzothiophene > 4,6-dimethyldibenzothiophene > thiophene for the SCCs and pyridine > quinoline > indole > acridine for the NCCs. The composite material exhibited chemical stability, mechanical strength and recyclability for both the model oil and the real FCC oil. It is an active heterogeneous adsorbent for heterocyclic SCCs and NCCs with a high selectivity for aromatics. By using 2 g of this material, 97.4% (Ci = 77 ppmwN) and 58.3% (Ci = 350 ppmwS) for NCCs and SCCs, respectively, were removed from 20 g of real FCC oil in 2 h at ambient conditions. The main factors accountable for this excellent adsorption are the multiporous structure of the material with its enhanced surface area and porosity, its unique structural interactions, specific pore size and the presence of unsaturated Lewis acid metal (Al) sites.

Experimental research on selective adsorption of gaseous mercury (II) over SiO2, TiO2 and γ-Al2O3

Solid selective adsorption to partition mercury speciation (Hg0, Hg2+) in flue gas is known as the innovative technology in developing solid agents application in online measurement of mercury speciation by continuous emission monitoring system (Hg-CEMS). Porous materials SiO2, TiO2 and γ-Al2O3 were chosen as the selective adsorbents and the systematical experiments were conducted in a fixed-bed reactor. Adsorption tests indicated that Hg0 was scarcely adsorbed by these three porous adsorbents while Hg2+ exhibited an apparent adsorption behavior. γ-Al2O3 was verified to be efficient in Hg2+/Hg0 separation because of its high HgCl2 adsorption capacity and SO2 anti-interference ability. The intrinsic mechanisms of HgCl2 selective adsorption and SO2 competition over γ-Al2O3 surface sites were further investigated. Temperature programmed desorption (TPD) analyses demonstrated that the weak interaction between Hg0 and γ-Al2O3 surface was ascribed to a physisorption manner while the adsorption of HgCl2 was characterized chemical bonding. Hydroxyl (Al-OH), Lewis Aln+-Bronsted On− pairs and the coordinatively unsaturated oxygen (O2− ions) were deduced to be effective basic sites for the chemisorption of HgCl2 on γ-Al2O3. Simultaneously, the competitive adsorption between SO2 and HgCl2 in O2− ions was confirmed to be responsible for the increased breakthrough of HgCl2 over γ-Al2O3 layer with the existence of SO2.

Heterogeneous reaction of Cl2 and NO2 on γ-Al2O3: A potential formation pathway of secondary aerosols

The importance of the oxidizing capacity of reactive chlorine species, and the heterogeneous reactions of atmospheric pollution gases on the surface of particles has been well established in field observation, modeling simulation and laboratory exploration. However, less is known about the reactions of reactive chlorine on mineral particles. We studied the effect of Cl2 on the heterogeneous reaction of NO2 with γ-Al2O3 by using ion chromatography and positron annihilation lifetime spectroscopy. The presence of Cl2 can promote the uptake of NO2 on γ-Al2O3 at humid conditions. The probable explanations are that Cl2 rapidly reacts with NO2 on the γ-Al2O3 surface in the presence of adsorbed water, and nitrites, as the intermediate products during the heterogeneous reaction of NO2 on mineral dust, are immediately oxidized by adsorbed Cl2. In the positron annihilation lifetime spectroscopy experiment, a porous γ-Al2O3 was demonstrated by the relatively high fourth lifetime intensity. The increase in the number of anions (onto γ-Al2O3) when the reaction time was prolonged was a direct consequence of the decrease in the o-Ps intensity and the o-Ps lifetime, which illustrated that the heterogeneous reactions might occur on the porous surface of γ-Al2O3. Our results suggest that the oxidative effect of Cl2 on the heterogeneous conversion of NO2 to nitrogen-containing particles might have a significant contribution to the fine particle growth and to the unknown sources of nitrate observed in secondary inorganic aerosols.

Hierarchically porous γ-Al2O3 nanosheets: Facile template-free preparation and reaction mechanism for H2S selective oxidation

A template-free strategy has been developed for the controlled synthesis of hierarchically porous γ-Al2O3 with three dimensional (3D) “cluster-like” architectures assembled from 2D nanosheets (∼15 nm thick). This unique structure endows the material with large active surface area, high accessibility and ready mass transport ability, capable of promoting the catalytic performance. As a result, the designed γ-Al2O3 exhibits high activity for selective oxidation of H2S to elemental sulfur. All the porous γ-Al2O3 samples show outstanding sulfur selectivity (∼100%) below 200 °C. At higher temperatures, the H2S conversion increases while the sulfur selectivity decreases. The maximum sulfur yield (93%) can be achieved over the optimal sample at 240 °C, which is much higher than those of commercial alumina and most of the reported alumina-based catalysts. The structure–activity relationship of the catalysts has been systematically studied. It is demonstrated that the surface acidity of the γ-Al2O3 has a great influence on catalytic activity. By means of pyridine and H2S in situ FTIR, the nature of the active sites as well as the reaction mechanism of H2S selective catalytic oxidation over γ-Al2O3 is revealed, providing important insights into the design of alumina-based materials for the removal of sulfur-containing compounds.

Enhanced Hydrothermal Stability of γ-Al2O3 Catalyst Supports with Alkyl Phosphonate Coatings.

In this study, monolayers formed from organophosphonic acids were employed to stabilize porous γ-Al2O3, both as a single component and as a support for Pt nanoparticle catalysts, during exposure to hydrothermal conditions. To provide a baseline, structural changes of uncoated γ-Al2O3 catalysts under model aqueous phase reforming conditions (liquid water at 200 °C and autogenic pressure) were examined over the course of 20 h. These changes were characterized by X-ray diffraction, NMR spectroscopy, N2 physisorption, and IR spectroscopy. It was demonstrated that γ-alumina was rapidly converted into a hydrated boehmite (AlOOH) phase with significantly decreased surface area. Deposition of alkyl phosphonate groups on γ-alumina drastically inhibited the formation of boehmite, thereby maintaining its high specific surface area over 20 h of treatment. 27Al MAS NMR spectra demonstrated that hydrothermal stability increased with alkyl tail length despite lower P coverages. Although the inhibition of boehmite formation by the phosphonic acids was attributed primarily to the formation of Al2O3-PO x bonds, it was found that use of longer-chain octadecylphosphonic acids led to the most pronounced effect. Phosphonate coatings on Pt/γ-Al2O3 improved stability without adversely affecting the rate of a model reaction, catalytic hydrogenation of 1-hexene.

Template-free synthesis of hierarchical meso-macroporous γ-Al2O3 support: Superior hydrodemetallization performance

The design of hierarchically porous catalytic supports is considered as one of the most efficient strategies to achieve efficient mass transport and thus high catalytic performance in heterogeneous catalysis. As one of the most important catalytic supports, facile synthesis of γ-Al2O3 with hierarchical porosities is of great industrial importance. In this paper, nest-like hollow γ-AlOOH microspheres constructed from numerous hierarchically organized nanowires were synthesized via a template-free simple hydrothermal approach, from which hierarchically porous γ-Al2O3 microspheres with average macropores of 900nm, mesopores of 20nm and a pore volume of 0.93cm3/g were obtained readily. Due to their structural merits, such nest-like γ-Al2O3 microspheres could serve as excellent catalytic support. As a demonstration, a MoNi/γ-Al2O3 supported catalyst was prepared, which was applied for hydrodemetallization (HDM) catalysis. Compared with the catalyst prepared with the commercial γ-Al2O3, our catalyst exhibits superior catalytic performance and longer life due to enhanced diffusion of the reactants.

Efficient Transformation of Waste Bone Oil into High Quality Biodiesel via a Synergistic Catalysis of Porous Organic Polymer Solid Acid and Porous γ-Al2O3-K2O Solid Base

We report here a novel synergistic catalysis system combined with porous organic polymeric solid acid (H-PDVB-SO3H) and K2O doped porous γ-Al2O3 solid base (γ-Al2O3-K2O). H-PDVB-SO3H and γ-Al2O3-K2O have abundant nanopores, controllable surface wettability, and high concentrations of acidic and basic sites. The synergistic catalysis system exploited by us could efficiently transform acidulated bone oil and plant oil into high quality biodiesel under mild conditions, which achieved ASTM specifications pertaining to acid number and total and free glycerin. Acidulated bone is a bone meal treated with sulfuric acid containing high-value hydrocarbons, which is generated in large amounts by the cattle industry. This work develops an efficient and cost-effective approach to transform animal waste into high quality biodiesel.

Optimization of solvent-free mechanochemical synthesis of Co/Al2O3 catalysts using low- and high-energy processes

In this work, alumina-supported cobalt (Co/Al2O3) catalysts were prepared using new solvent-free mechanochemical synthesis methods: low-energy vibratory ball milling (Fritsch, Pulverisette 0) and high-energy planetary ball milling (Retsch, PM 100). γ-Al2O3 supports and Co/Al2O3 catalysts after mechanochemical treatments were characterized using a combination of techniques. The study of solid particles revealed the abrasion and fragmentation phenomena of porous γ-Al2O3 particles and pore filling under milling. Functional cobalt particles introduced by the mechanochemical synthesis were observed to be preferentially localized on the outer surface of the alumina supports. High Fischer–Tropsch reaction rates were obtained with the catalysts prepared by optimized mechanochemical synthesis conditions. The enhanced catalytic performance can be attributed to the relatively high dispersion of cobalt and the absence of inert cobalt aluminates which are usually present in the catalysts synthesized by the conventional impregnation.

Novel application of red mud: Facile hydrothermal-thermal conversion synthesis of hierarchical porous AlOOH and Al2O3 microspheres as adsorbents for dye removal

Originated from the by-product of alumina production, red mud has caused severe impact on environment. To cope with the increasingly urgent environmental issue, red mud has now been utilized for the first time to obtain the hierarchical porous γ-AlOOH/γ-Al2O3 microspheres as high efficient adsorbents for dye removal. The NaAlO2 leached from the red mud is hydrothermally treated at 150°C for 6.0h in the presence of urea, leading to hierarchical porous γ-AlOOH microspheres, with a specific surface area of 76.8m2g−1, 93% of which have a diameter within the range of 3.5–7.5µm. The subsequent mild thermal conversion at 600°C for 2.0h results in the hierarchical porous γ-Al2O3 microspheres with a specific surface area of 158.6 m2 g−1, and ca. 92% of which bear a size of 3.0–7.0µm. The porous γ-AlOOH and γ-Al2O3 microspheres exhibit excellent adsorption for MB with the maximum adsorption capabilities of 953.0mgg−1 and 1587.6mgg−1, respectively, and the latter is distinctly higher than most of the reported results. The possible formation is proposed, and the adsorption mechanism is discussed. The present work provides a new insight into the comprehensive utilization of the red mud as great potential adsorbents for removal of anionic dyes from mimetic waste water, and also is helpful for the future potential applications of the unique hierarchical porous structures in catalysis and other related fields.

Novel three-dimensional flower-like porous Al 2 O 3 nanosheets anchoring NiS 2 nanoparticles for high-efficiency hydrogen evolution

In this contribution, we report unique flower-like porous γ-Al2O3 nanosheets anchoring uniform NiS2 nanoparticles, which are firstly fabricated through a common hydrothermal process and two-step calcinations. Different from the general strategy, the flower-like NiS2@Al2O3 are directly prepared by the precursor of Ni2Al(CO3)2(OH)3 nanosheets rather than adding Al2O3 coating later. This novel nanoarchitecture can efficiently disperse and confine the active nanoparticles, which can not only offer large specific surface area, but also hinder aggregation and peeling off from the substrates, thus to demonstrate superior HER activities, especially the long-time stability. In this work, the as-synthesized composite exhibits an onset potential of −126 mV and excellent durability of 3% decrease in potential at constant current of 10 mA/cm2 for 48 h.

Atomic Layer Deposition of Iron Sulfide and Its Application as a Catalyst in the Hydrogenation of Azobenzenes.

The atomic layer deposition (ALD) of iron sulfide (FeSx ) is reported for the first time. The deposition process employs bis(N,N'-di-tert-butylacetamidinato)iron(II) and H2 S as the reactants and produces fairly pure, smooth, and well-crystallized FeSx thin films following an ideal self-limiting ALD growth behavior. The FeSx films can be uniformly and conformally deposited into deep narrow trenches with aspect ratios as high as 10:1, which highlights the broad applicability of this ALD process for engineering the surface of complex 3D nanostructures in general. Highly uniform nanoscale FeSx coatings on porous γ-Al2 O3 powder were also prepared. This compound shows excellent catalytic activity and selectivity in the hydrogenation of azo compounds under mild reaction conditions, demonstrating the promise of ALD FeSx as a catalyst for organic reactions.

Effects of electrical conductivity on the formation and annihilation of positronium in porous materials.

In this paper we show the preliminary evidence that the formation of positronium depends on the electrical conductivity of porous materials. Porous nano γ-Al2O3 was chosen as the base material, and it was filled with carbon of different allotropes (commercial graphite, carbon black, carbon nanotubes and home-made ordered mesoporous carbon) by a mechanical mixing method. The positron lifetime and Doppler broadening of the annihilation radiation were measured for these composites. In the pure γ-Al2O3 sample, there are two long positron lifetime components τ3 (3.5 ns) and τ4 (101.3 ns) with intensities of 1.0% and 24.6%, which indicates the formation and annihilation of positronium in small and large pores, respectively. In the carbon filled γ-Al2O3 samples, the longest lifetime τ4 and its intensity I4 both show a continuous decrease with increasing carbon content. The Doppler broadening S parameter shows a similar tendency to τ4 and I4. This suggests that carbon has a quenching effect on positronium and also inhibits the formation of positronium. Among these four carbon allotropes, carbon nanotubes have the strongest quenching and inhibition effect, while graphite has the weakest effect. A detailed study further reveals that the decreasing rate of τ4 and I4 as well as the S parameter depend on the electrical conductivity of the carbon filled γ-Al2O3 and also the specific surface area of the filled carbon. Our results suggest that the formation and annihilation of positronium are strongly affected by the electrical conductivity of the materials.

Synthesis of Highly Dispersed and Highly Stable Supported Au–Pt Bimetallic Catalysts by a Two-Step Method

Highly dispersed and highly stable supported bimetallic catalysts were prepared using a two-step process. Pt nanoparticles (NPs) were first deposited on porous γ-Al2O3 particles by atomic layer deposition (ALD). Au NPs were synthesized by using gold(III) chloride as the Au precursor, and then immobilized on ALD Pt/γ-Al2O3 particles. The Au–Pt bimetallic catalysts were highly active and highly stable in a vigorously stirred liquid phase reaction of glucose oxidation.

Highly active and stable alumina supported nickel nanoparticle catalysts for dry reforming of methane

A highly stable and extremely active nickel (Ni) nanoparticle catalyst, supported on porous γ-Al2O3 particles, was prepared by atomic layer deposition (ALD). The catalyst was employed to catalyze the reaction of dry reforming of methane (DRM). The catalyst initially gave a low conversion at 850°C, but the conversion increased with an increase in reaction time, and stabilized at 93% (1730Lh−1gNi−1 at 850°C). After regeneration, the catalyst showed a very high methane reforming rate (1840Lh−1gNi−1 at 850°C). The activated catalyst showed exceptionally high catalytic activity and excellent stability of DRM reaction in over 300h at temperatures that ranged from 700°C to 850°C. The excellent stability of the catalyst resulted from the formation of NiAl2O4 spinel. The high catalytic activity was due to the high dispersion of Ni nanoparticles deposited by ALD and the reduction of NiAl2O4 spinel to Ni during the DRM reaction at 850°C. It was verified that NiAl2O4 can be reduced to Ni in a reductive gas mixture (i.e., carbon monoxide and hydrogen) during the reaction at 850°C, but not by H2 alone.

Spark plasma sintering of ultra-porous γ-Al2O3

Nanocrystalline gamma alumina (γ-Al2O3) powder with a crystallite size of ~10nm was synthesized by oxidation of high purity aluminium plate in a humid atmosphere followed by annealing in air. Spark plasma sintering (SPS) at different sintering parameters (temperature, dwell time, heating rate, pressure) were studied for this highly porous γ-Al2O3 in correlation with the evolution in microstructure and density of the ceramics. SPS sintering cycles using different heating rates were carried out at 1050–1550°C with dwell times of 3min and 20min under uniaxial pressure of 80MPa. Alumina sintered at 1550°C for 20min reached 99% of the theoretical density and average grain size of 8.5µm. Significant grain growth was observed in ceramics sintered at temperatures above 1250°C.