Mesoporous γ-Al2O3 Research Articles

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.

Hydrothermally stable mesoporous ZrO2 membranes prepared by a facile nanoparticle deposition process

Stabilized ZrO2 membranes (e.g. 8YSZ) have great potential due to their excellent thermal stability. In this paper, we present a new synthetic methodology to produce 8YSZ membranes on commercial macroporous α-Al2O3 supports. The resulting membranes have an average pore size of ∼5 nm and ∼3 nm, respectively, and a thickness approaching 2 μm. In various harsh stability tests, these membranes were tolerant to hydrothermal conditions (300 °C, 15 bar), high temperature (700 °C), and a high pH (NaOH, pH 14, 80 °C). They also demonstrated a suitable MWCO (15000 Da PEG; <3000 Da PEG) and permeance (145 kg h−1 m−2 bar−1; 40–50 kg h−1 m−2 bar−1) for commercial ultrafiltration processes. Importantly, they can also be considered for the production of novel graded macro-/meso-/microporous membrane systems, replacing the widely used but unstable mesoporous γ-Al2O3 membranes. At the end of this paper, we demonstrate that the synthetic methodology presented is also useful for producing membranes of other promising materials, including stabilized CeO2.

Removal of toluene using ozone at room temperature over mesoporous Mn/Al2O3 catalysts

The catalytic oxidation of toluene with ozone at room temperature was carried out over hierarchically ordered mesoporous catalysts (CeO2 (meso), Mn2O3 (meso), ZrO2 (meso), and γ-Al2O3 (meso)) and Al2O3 with various textural properties and phases (γ-Al2O3 (meso), γ-Al2O3 (13 nm), and α-Al2O3) to examine the effects of the nature of the catalyst on the catalytic activity. The catalysts were characterized by N2-physisorption measurements, powder X-ray diffraction, temperature programmed reduction, X-ray photoelectron spectroscopy and scanning transmission electron microscopy with energy dispersive spectroscopy. Among the ordered mesoporous catalysts, γ-Al2O3 (meso) had the highest toluene removal efficiency because of its highest surface area and pore volume, which in turn was selected for further investigation. Manganese (Mn) was introduced to various Al2O3 to improve the toluene removal efficiency. Comparing the Mn-loaded catalysts supported on various Al2O3 with different crystalline phases or pore structures, Mn/γ-Al2O3 (meso), had the highest catalytic activity as well as the highest CO2/CO ratio. The higher activity was attributed to the larger surface area, weaker interaction between Mn and Al2O3, and larger portion of Mn2O3 phase. The increase in ozone concentration led to an improvement in the carbon balance but this enhancement was insufficient due to the deposition of by-products on the catalyst. After long term tests at room temperature, the reaction intermediates and carbonaceous deposits of the used catalysts were identified.

Preparation of Ni based mesoporous Al2O3 catalyst with enhanced CO2 methanation performance.

A Ni based mesoporous γ-Al2O3 (MA) catalyst was prepared via partial hydrolysis without organic surfactants and employed in the carbon dioxide methanation reaction. The obtained catalysts were characterized by N2 adsorption–desorption, H2-TPR, XRD, XPS, TG, SEM and TEM-EDS techniques. CO2 methanation was performed in a fixed-bed reactor. A high surface area of MA with excellent hydrothermal stability was obtained, which promoted the dispersion of nickel species, producing a better catalytic performance. Incorporation of more NiO species into the Ni/MA catalyst increased the amount of active metallic Ni sties, further improving the catalytic activity and CH4 selectivity. Moreover, the monolithic skeleton of MA with fabric-like walls suppressed the aggregation of active metallic Ni sites and carbon deposition, enhancing the catalyst's stability, which provides a new insight for potential industrial applications.

Promotional effect of Mg in trimetallic nickel-manganese-magnesium nanocrystalline catalysts in CO2 reforming of methane

In the present paper, the dry reforming reaction was studied over the 10 wt%Ni-3wt.%Mn-x wt.% Mg (x = 2, 4 and 6 wt%) catalysts supported on γ-Al2O3 with mesoporous structure. The physicochemical characteristics of the samples were determined by XRD, BET, TPO, and SEM techniques. Mesoporous γ-Al2O3 carrier with the high BET area (186 m2/g) was synthesized by a simple sol–gel method and the Ni, NiMn and Mg promoted catalysts possessed nanocrystalline mesoporous structure with the BET area in the range of 127–176 m2/g. The average pore radius of the prepared catalysts were smaller than 11 nm. All the synthesized samples exhibited a CH4 conversion in the range of 60–65% at 700 °C. The small differences in methane conversion in all catalysts could be related to the same nickel loading. According to the TPR results, the Mg addition caused an increase in the reducibility of the nickel catalyst and the Mg-promoted sample exhibited a higher conversion compared to the monometallic catalyst, due to its higher reducibility. The results showed that the textural characteristics of the catalysts were affected by the content of Mg. The results indicated that the NiMn/Al2O3 catalyst promoted by 4 wt% Mg showed the highest CH4 conversion in all studied reaction temperatures (550–700 °C). Furthermore, only one oxidation peak was detected for all catalysts in TPO analysis, which was related to the filamentous form carbon. The 10Ni/Al2O3 and 10Ni3Mn4Mg/Al2O3 catalysts exhibited the highest and the lowest amount of deposited filamentous carbon, respectively. The 10Ni3Mn4Mg/Al2O3 catalyst was stable during the 20 h time on stream without any decline in CH4 conversion.

Initial Steps toward the Development of Grafted Ionic Liquid Membranes for the Selective Transport of CO2

This work reports on a promising strategy for the development of novel grafted ionic liquid membranes (GILMs) in which phosphonate-based ILs are confined within the pores of a mesoporous γ-Al2O3 ceramic membrane by chemical grafting. The effect of both the chemical nature (i.e., alkyl versus ether) of the organic spacer chain and the presence of phosphonate coupling functions were evidenced as crucial parameters influencing CO2 transport through the membranes. The effectiveness of the grafting procedure yielding GILMs was clearly demonstrated by Fourier transform infrared spectroscopy and high resolution-magic angle spinning NMR, and attractive membrane performance was evidenced through both the CO2/N2 ideal selectivity (∼140) and CO2 permeability (∼130 Barrer).

Ce-modified mesoporous γ-Al2O3 supported Pd-Pt nanoparticle catalysts and their structure-function relationship in complete benzene oxidation

In this investigation, a mesoporous γ-Al2O3 with large surface area and good thermal stability was synthesized and employed as the support for preparing a series of Pd-Pt nanocrystalline catalysts by using a high-temperature solution-phase reduction method. The PdOx (x = 0, 1) and PtOx (x = 0, 2) nanoparticles were found to have a small diameter (about 2 nm) and were highly dispersed on the surface of the mesoporous γ-Al2O3. The results show that catalysts with the appropriate ceria greatly improved the physical adsorption/chemisorption of benzene to Pd-Pt nanocrystals, which greatly enhanced the activity to achieve the complete oxidation of benzene. The high activity of the catalyst was mainly due to the nano-effects of Pd-Pt nanocrystals and the interactions among the active components. 0.2%Pd-Pt(1:1)/10%Ce/γ-Al2O3 demonstrated the best activity for the complete oxidation of benzene at 200 °C. Furthermore, this catalyst maintained 95% benzene conversion for 1000 h at 190 °C and displayed good resistance to water and Cl-poisoning, which indicated that the Pd-Pt nanocrystalline catalysts have promise for adoption by the industry.

Tailoring the structure of Co-Mo/mesoporous γ-Al2O3 catalysts by adding multi-hydroxyl compound: A 3000 kt/a industrial-scale diesel ultra-deep hydrodesulfurization study

Ever-increasing concern on environmental impacts (e.g., sulfur pollution) by fossil fuels has triggered the research on hydrodesulfurization (HDS). In this work, Co-Mo nanoparticles were deposited on the mesoporous γ-Al2O3 support with the addition of organic compound, and the physico-chemical properties of the catalysts (Co-Mo-C/mesoporous γ-Al2O3) were then characterized by multi-techniques such as H2-TPR, HRTEM, XPS, N2 physisorption. It is found that the Co-Mo-C/mesoporous γ-Al2O3 catalyst is easier to be reduced when organic compound is added, enhancing the sulfuration. This results in better dispersion of Co-Mo-S species and more Co-Mo-S II active sites, which significantly enhance diesel ultra-deep hydrodesulfurization activity. Furthermore, this novel catalyst was also tested for HDS reaction in a 3000 kt/a industrial-scale plant. Gratifyingly, this catalyst showed effective reduction of sulfur content from 9000 to less than 10 μg/g and also high stability over 5000 h. The results are of great significance to the design and development of industrial HDS catalysts.

Green synthesis of mesoporous γ-Al2O3 from coal fly ash with simultaneous on-site utilization of CO2.

Mesoporous Al2O3 with crystalline framework walls has expanded all over the world due to the various potential applications especially in catalysis. Here, we develop a green and facile approach for the conversion of coal fly ash (CFA) into ordered mesoporous γ-Al2O3. The practical and promising lime-sinter method was comprehensively studied for the extraction of aluminum from CFA as a first step. The extraction efficiency of aluminum could reach up to 87.42%, through calcining with CaCO3 at 1390°C for 1 h and then dissolving in Na2CO3 solution at 70°C for 0.5 h. Combined with the urgent demand for CO2 emission reduction, simulated purified flue gas was introduced to precipitate the Al(OH)3 precursors without structure-directing agents for just 1 h, followed by calcining at only 400°C or 550°C. A series of characterizations were conducted to discuss the effect of precipitation temperature and calcination temperature, resulting the superior product (Al2O3-65/550) with high surface area (230.3 m2 g-1), crystalline γ-Al2O3 phase and ordered mesostructure. This proposed strategy, integrating the on-site recycling of CFA and utilization of CO2, appears to be promising for scalable production of mesoporous γ-Al2O3.

Synthesis of Mesoporous γ-Al₂O₃ with Spongy Structure: In-Situ Conversion of Metal-Organic Frameworks and Improved Performance as Catalyst Support in Hydrodesulfurization.

Over the past decades, extensive efforts have been devoted to modulating the textural properties, morphology and microstructure of γ-Al2O3, since the physiochemical properties of γ-Al2O3 have close correlations with the performance of hydrotreating catalysts. In this work, a spongy mesoporous γ-alumina (γ-Al2O3) was synthesized using Al-based metal-organic frameworks (Al-MOFs) as precursor by two-step pyrolysis, and this Al-MOF-derived γ-Al2O3 was used as hydrodesulfurization (HDS) catalyst support, to explore the effect of support on the HDS performance. Compared with industrial γ-Al2O3, the spongy alumina displayed well-developed porosity with relatively high surface area, large pore volume, and abundant weak Lewis acid sites. Based on catalyst characterization and performance evaluation, sulfurized molybdenum and cobalt molecules were able to incorporate and highly disperse into channels of the spongy mesoporous alumina, increasing the dispersion of active catalytic species. The spongy γ-Al2O3 was also able to enhance the diffusion efficiency and mass transfer of reactant molecules due to its improved texture properties. Therefore, the corresponding catalyst presented higher activities toward HDS of dibenzothiophene (DBT) than that from industrial alumina. The spongy mesoporous γ-alumina synthesized by Al-MOFs provides a new alternative to further develop novel γ-alumina materials with different texture and various nanoporous structures, considering the diversity of MOFs with different compositions, topological structures, and morphology.

Magnetic mesoporous γ-Al2O3/ZnFe2O4 micro-bowls realizing enhanced adsorption, separation and recycle performance towards waste water

Magnetic mesoporous γ-Al2O3/ZnFe2O4 micro-bowls have been synthesized via a simple sol-gel route combining spray-drying technique, in which block copolymer P123 was used as the soft template and aluminum isopropoxide was aluminum source. This mesoporous γ-Al2O3/ZnFe2O4 composite possesses bowl-like structure, high specific surface area (316 m2 g−1), large pore volume (0.936 mL g−1), and fair magnetism (1.45 emu·g−1). As a demonstration, this γ-Al2O3/ZnFe2O4 composite was served to remove Congo Red (CR) from simulated dye stuffs wastewater. The maximum adsorption capacity of γ-Al2O3/ZnFe2O4 micro-bowls for CR was up to 413 mg g−1, which is much higher than most of the reported magnetic absents. The kinetic data related to the adsorption of CR match well with the pseudo-second-order kinetic model. And the CR adsorption isotherm can be evaluated using Langmuir model. Moreover, the magnetic micro-bowls could be simply separated and cyclic utilized from the waste water by magnetic attraction after adsorption.

Confinement of microporous MOF-74(Ni) within mesoporous γ-Al2O3 beads for excellent ultra-deep and selective adsorptive desulfurization performance

The microporous MOF-74(Ni) was impregnated on mesoporous γ-Al2O3 beads leading to successful formation of a hierarchical multiporous composite MOF-74(Ni)@γ-Al2O3 containing 10 wt% MOF-74(Ni) via solvothermal method. The confinement effect introduced by the channels of γ-Al2O3 beads resulted in ultrathin continuous films of MOF-74(Ni) which has significantly enhanced the surface area and surface utilization rate by ca. 16%. The composite showed excellent adsorptive desulfurization in the order of dibenzothiophene (DBT) ≈ benzothiophene (BT) > 4,6-dimethyldibenzothiophene > 3-methyl thiophene and was applied efficiently for ultra-deep adsorptive desulfurization. The 35 ppmwS concentrations of DBT and BT in model oil were decreased down to 2.30 ± 0.20 and 4.28 ± 0.31 ppmwS, respectively, with high selectivity. The reason behind excellent ultradeep desulfurization and high selectivity of S-heterocycles over aromatics is utilization of available unsaturated metal and strong metal-S bonding. In addition, the high mechanical and chemical stability of millimeter-sized composite enabled the easy recyclability with excellent efficiency and high fluidity. All the above excellency shall endow the composite to apply potentially in practical (especially ultra-deep) adsorptive desulfurization process.

Synergistic effects in iron-copper bimetal doped mesoporous γ-Al2O3 for Fenton-like oxidation of 4-chlorophenol: Structure, composition, electrochemical behaviors and catalytic performance

Iron-copper bimetal supported on mesoporous γ-Al2O3 with different Fe/Cu ratios was prepared via a modified evaporation-induced self-assembly method and employed to degrade 4-chlorophenol (4-CP) in a Fenton-like process. The X-ray photoelectron spectroscopy, X-ray diffraction spectrum and UV–vis diffuse reflectance spectroscopy results confirmed the co-doping of Fe2+/Fe3+ and Cu+/Cu2+ into the lattice of γ-Al2O3 through the bonds of AlOFe and AlOCu. With the iron and copper co-doped in γ-Al2O3, three-fold oxygen vacancies (V0) could be achieved compared with that of non-metal catalysts, which was favorable for the reduction of iron and copper species. The 1Fe3Cu-γ-Al2O3 with a Fe/Cu mass ratio of 1:3 exhibited the highest activity on Fenton-like degradation of 4-CP due to the synergistic effects of Fe and Cu by facilitating the electron transfer in the recycles of Cu+/Cu2+ and Fe2+/Fe3+ based on the results of X-ray photoelectron spectroscopy, cyclic voltammetry and electro paramagnetic resonance analysis. The utilization efficiency of H2O2 was as high as 86.0% when 4-CP almost disappeared (i.e., 99.7 percent of 0.78 mM 4-CP) at 240 min and pH 7.0, additionally, their dechlorination and TOC removal efficiencies were 92.0% and 81.6%, respectively. The catalyst also displayed a good performance after 5th cycles. Furthermore, a possible mechanism for activation of OH on the catalyst surface was also proposed.

Organics Wastewater Degradation by a Mesoporous Chromium-Functionalized γ-Al2O3 with H2O2 Assistance

In this study, a mesoporous chromium-functionalized γ-Al2O3 (Cr/γ-Al2O3) catalyst was prepared by an impregnation method, and the catalytic activity was evaluated by the degradation of organics wastewater. The prepared catalyst was characterized by X-ray photoelectron spectroscopy, X-ray diffraction, nitrogen adsorption-desorption experiments, and scanning electron microscopy. The characterization results confirmed that the pores in the Cr/γ-Al2O3 catalyst distributed broadly in the mesoporous region, and the active chromium species were highly dispersed on the catalyst surface. The catalytic activity tests showed that the Cr/γ-Al2O3 catalyst exhibited a superior performance for the degradation of organics wastewater with H2O2 assistance. And the methylene blue (MB) disappeared within 20 min and the COD removal reached 76.5% within 40 min for the MB-simulated wastewater; for the phenol-simulated wastewater, the phenol removal was above 95% and the corresponding COD removal reached 71% within 40 min. Such an excellent catalytic performance demonstrates that the Cr/γ-Al2O3 catalyst has a potential application in the degradation of complex organics wastewater simultaneously.

Efficient catalyst recovery systems based on Pd-coated γ-alumina particles

Spherical mesoporous γ-Al2O3 (γ-Al) particles, embedded with magnetite nanoparticles (MNPs), were successfully prepared using a novel approach combining sol-gel and spray pyrolysis methods. Due to the magnetism of the embedded MNPs, the MNP/γ-Al particles can be utilized as recyclable catalyst supports. To demonstrate their recovery efficacy, Pd nanoparticles were impregnated on the surface of the MNP/γ-Al particles using the wetness impregnation method, and the resulting Pd/MNP/γ-Al catalysts were used to catalyze hydrogenation reactions of 4-nitrophenol. We demonstrated that when the magnetic nanoparticles were embedded in the catalysts, the recovery efficiency of the catalysts was further improved under the magnetic field.

Ordered mesoporous γ-Al2O3 as highly efficient and recyclable catalyst for the Knoevenagel reaction at room temperature

Coumarins are important class of organic compounds and intensively used in agricultural and pharmaceutical industries. We have developed a strategy for the synthesis of coumarin derivatives quantitatively via Knoevenagel condensation reaction of an ortho-hydroxyaryl aldehyde and an activated methylene compounds in the presence of ordered mesoporous γ-Al2O3 as a heterogeneous catalyst. The catalyst has been thoroughly characterized through powder X-ray diffraction, N2 sorption analysis, FTIR spectroscopy, TG/DTA, NH3-TPD and CO2-TPD (temperature programmed desorption) analysis. The material possesses periodicity in mesopores and both surface acidic and basic sites having strengths of 1.47 and 1.11 mmol g−1, respectively, which is highly favorable for carrying out the Knoevenagel condensation reaction for the synthesis of a wide range of condensation product (yields ∼98%) under very mild conditions. This amphoteric catalyst exhibits good surface Lewis acidity/basicity and high recyclability up to sixth reaction cycles without any significant loss in the product yield.

Post-combustion CO2 capture: On the potentiality of amino acid ionic liquid as modifying agent of mesoporous solids

In this paper, mesoporous γ-Al2O3 was impregnated with [Emim][Gly] ionic liquid (IL) at different loadings (5, 9 and 16% wt). The obtained sorbents were tested for CO2 capture under typical conditions of combustion flue-gas at temperatures varying in the range 303–373 K. N2 porosimetric analysis on the samples, coupled with kinetic tests of CO2 adsorption, revealed that a lower pore volume occurring at the highest IL loading ended up in a slower saturation process. The enhancement of CO2 capture capacity of the raw sorbent was monotonic with the IL loading and the best results were achieved at 303 K. The chemisorption nature of the adsorption process for IL-containing sorbents was assessed by means of FT-IR analysis. Finally, preliminary tests of cyclic adsorption/desorption showed that nearly 80% of the original CO2 capture capacity of sorbent was restored by steam desorption at 388 K.

Preparation and characterization of mesoporous γ-Al2O3 recovered from aluminum cans waste and its use in the dehydration of methanol to dimethyl ether

The present study includes synthesis of two γ-Al2O3 samples from waste aluminum cans using a simple precipitation method. Precipitation was carried out using two different precipitating agents (i.e. NaOH and NH4OH). The two prepared alumina samples were characterized by means of X-ray diffraction (XRD) and N2 adsorption–desorption techniques. Surface acidity of γ-Al2O3 samples was measured by adsorption of two different probe molecules (i.e. pyridine and dimethyl pyridine) followed by desorption measurements using thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Catalytic activity of the two prepared alumina samples towards the dehydration of methanol (to dimethyl ether) was studied in a fixed bed reactor at 300 °C. For comparison reasons, commercial γ-Al2O3 sample was, also, tested for the same catalytic reaction under the same conditions. Results showed that the alumina sample prepared using NaOH as a precipitating agent exhibited a better catalytic activity and stability compared with that prepared using NH4OH and showed a similar activity as the commercial γ-Al2O3 sample.

A Novel Synthesis Route of Mesoporous γ-Alumina from Polyoxohydroxide Aluminum

Mesoporous gamma-aluminas (γ-Al2O3) were synthesized starting from an unusual precursor of polyoxohydroxide aluminum (POHA). This precursor was obtained from aluminum oxidation in alkaline water-ethanol solvent in the presence of d-glucose that induces the formation of a gel, which leads to the POAH powder after ethanolic treatment. Precipitated POHAs were calcined at different temperatures (300, 400, 700 and 900 °C) resulting in the metastable γ-Al2O3 phase. Whereas at 300 °C no γ-Al2O3 phase was formed, unexpectedly, mesoporous γ-Al2O3 was obtained at 400 oC having a high specific surface area (282 m2/g) and a narrow pore size distribution. At higher temperatures, the aluminas had the expected decrease in surface area: 166 m2/g (700 °C) and 129 m2/g (900 °C), respectively. The structural change from POHA to alumina calcined at 400 oC occurs directly without the need to isolate the hydroxide or oxyhydroxide aluminum precursors. Both POHA and transition aluminas were characterized by Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), N2 sorption and Scanning Electron Microscopy (SEM). These findings show an alternative route to produce high standard aluminas.

Characterization of a mesoporous γ-Al2O3 catalyst: Influence of their properties on ethanol conversion

A mesoporous alumina has been synthetized by a hydrothermal method describe by Ĉejka and al. who use as precursor an aluminium isopropoxide and subsequently calcining the precipitate obtained in nitrogen flow at 683 K for 6h. The structural and morphological study evidence that the alumina obtained is a thermal stable γ-Al2O3 phase up to 1073 K with a specific surface area value of 174 m2g-1.The study of the surface hydroxyl groups in the sample γ-Al2O3 phase calcined at 1073 K (hereinafter called ALMP1073) reveals the presence of three types of active OH groups absorbing at 3787, 3725 and 3690 cm-1 and that they are significantly acidic, but not enough to protonate pyridine., i.e, they can be considered as Lewis acid.Catalytic test in ethanol dehydration prove that the ALMP1073 sample is active and selective in the dehydration of ethanol to diethylether in the range 523-573 K, as well as in the dehydration of ethanol to ethylene in the range 623-723 K These data are consistent with those obtained by infrared spectroscopy.The ethoxy groups formed on the surface of γ-Al2O3 are proposed as intermediate species in the ethanol dehydration reaction for both diethylether and ethylene formation.