Commercial γ-Al2O3 Research Articles

The key role played by mesoporous alumina as binder for obtaining ultra-hard CaO based pellets for thermochemical heat storage leveraging the CaO/CaCO3 cycle

The synthesis of CaO-based pellets with high energy storage and suitable mechanical resistance after prolonged cycling is pivotal for the successful implementation of the Calcium looping (CaL) technology for energy storage in CSP plants. In this work, CaO-based spherical pellets (CAA) were prepared made up of 60 wt % Ca(OH)2 and varying ratios (0–40 wt %) of commercial γ-Al2O3 and mesoporous γ-Al2O3 (m-Al2O3). They were tested in TG in several CO2 carbonation/decarbonation cycles (15 and 50 for selected pellets) and their respective average crushing strengths measured. After 15 cycles, the optimum pellet CAA 20-20 (60 wt % Ca(OH)2/20 wt % γ-Al2O3/20 wt % m-Al2O3) exhibits a remarkable energy storage density of 1030 kJ/kg with a superb crushing strength of ∼29 N. This was ascribed to the enhanced formation of the calcium aluminate mayenite (Ca12Al14O33), since the high BET surface area (384 m2 g−1) of mesoporous γ-Al2O3 promotes the interaction with calcium oxide. Additionally, CAA 20-20 showed meaningful porosity that favored CO2 mass transport. Interestingly, after 50 cycles, the optimum CAA 20-20 pellet maintained a high carbonation yield (0.46), representing an 84 % of the initial value and corresponding to an energy storage density of ∼873 kJ/kg. Additionally, the optimum CAA 20-20 pellet was coated with an external layer of Al-MCM-41 silica that augmented its crushing strength up to 37 N, with a concurrent slight abatement in the carbonation yield and energy storage density after 50 cycles (0.43 and ∼824 kJ/kg). Consequently, both uncoated and coated CAA 20-20 pellet are promising for the successful implementation of CaL in CSP plants.

Upgrading of plastic waste-derived wax through air gasification using promoted Ni/Al2O3 catalysts for H2 generation

Catalytic air gasification of plastic waste-derived wax (PW) was performed using Ni/X-Al2O3 (X = Ti, Sr, or La) catalysts to produce H2-rich gas for the first time. For this purpose, X-Al2O3 supports were primarily synthesized by doping different promoters into the Al2O3 structure, followed by the loading of Ni. The catalytic performances of prepared catalysts were compared with that of 10Ni/Al, prepared by impregnation of Ni into commercial γ-Al2O3. Compared with using 10Ni/Al, the use of Ni/X-Al2O3 catalysts resulted in higher activity and selectivity, wherein the highest gas yield (74.78 wt%) and H2 selectivity (25.30 vol%) were achieved using 10Ni/5Ti-Al. Also, the coke yield effectively decreased when using Ni/X-Al2O3 catalysts, particularly 10Ni/5Ti-Al, compared with using 10Ni/Al. These findings are ascribed to the versatile effects of well-dispersed metallic Ni active sites, increased density of Lewis acidic sites at the expense of Brønsted acid sites, and enhanced oxygen transfer capacity of the catalyst owing to Ti addition. Moreover, increasing the concentrations of Ni (up to 10 %) and Ti (up to 5 %) enhanced the catalytic activity and selectivity for H2 production. Increasing the temperature (up to 750 °C) showed a positive effect on the production of H2-rich gas. Furthermore, varying the catalyst-to-feedstock ratio affected the gas yield and H2 selectivity.

Sustainable production of aromatic-rich biofuel via catalytic co-pyrolysis of lignin and waste polyoxymethylene over commercial Al2O3 catalyst

Co-valorization of biomass and multiple solid wastes is essential to environment protection and energy security. Herein, aromatic-rich biofuel was produced from lignin and waste polyoxymethylene (POM) via catalytic co-pyrolysis process. Commercial and cheap γ-Al2O3 catalyst exhibited good catalytic performance. Series characterizations and bench-top pyrolysis experiments were conducted to illustrate the synergism between raw materials and the mechanism of aromatics formation. The TG analysis and thermodynamics calculation revealed that a remarkably positive synergistic effect existed between lignin and POM, which reduce the activation energies and make the reaction more conducive in terms of thermodynamics. Meanwhile, the yields of biochar and bio-oil increased considerably. Additionally, the operating conditions affected the product distributions significantly. The suitable mixing ratio of lignin to POM was around equal (5:5) with the bio-oil yield increased to 28.3 % and aromatic hydrocarbons selectivity increased to > 95 %. Moreover, POM, the precursor for alkylating reagents and hydrogen donors, could promote the deoxygenation reactions of phenolic intermediates and result into aromatic hydrocarbons. The acid sites of γ-Al2O3 promoted series secondary cracking reactions (alkylation, deoxygenation), and thus improved bio-oil quality. Finally, the stability test showed that commercial γ-Al2O3 catalyst was slightly deactivated after 4 cycles because of coke deposits and acid sites loss.

The catalytic performance of FexMn1-xWO4 as novel wolframite-type nanocatalysts for the selective dehydration of methanol into dimethyl ether

Selective production of dimethyl ether (DME), as a second-generation biofuel, under mild green conditions is still a challenge. Herein, FexMn1-xWO4 wolframite-type materials were proposed for the first time as efficient, selective, and stable catalysts towards methanol dehydration into DME. A simple one-step co-precipitation approach was used to fabricate the nanocomposites, and their catalytic performances were evaluated in comparison to earlier studies and to the commercial γ-Al2O3 in terms of activity. The catalysts’ structure, morphology, and porosity were identified by XRD, XPS, FTIR, TEM, and N2-sorption analyses. Results of XRD and XPS confirmed the successful synthesis of FexMn1-xWO4 catalysts. Acidity of these nanocomposites were greatly influenced with the variation in x-value, calcination temperature, and doping with SO42−. The Brønsted characters of the acid sites and their weak and medium strength were investigated from PY-FTIR, chemisorption of basic probes and pyridine-TPD. The variation of the catalytic activities of these nanocomposites was strongly correlated to the variation in the catalyst acidity. The catalytic activity results indicated that Fe0.5Mn0.5WO4 catalyst calcined at 500 °C and modified with 5 wt.% of SO42- is the most effective nanocomposite with conversion values of 86 and 90% at reaction temperatures of 250 and 275 °C, respectively and all of 100% DME selectivity. The remarkable enhancement in the catalytic activity due to the doping with SO42- is attributed to the inductive effect of S = O group created on the catalyst surface. This nanocomposite could be regenerated many times with nearly the same efficiency and selectivity. Moreover, it offered a long-term stability (∼120 h) towards DME production.

Sub-nanometer Pt2In3 intermetallics as ultra-stable catalyst for propane dehydrogenation

Pt-based catalysts are the typical industrial catalysts for propane dehydrogenation (PDH), which still suffer from insufficient long-term durability due to the structural instability and coke deposition. A commercial γ-Al2O3 supported thermally robust sub-nanometer Pt2In3 intermetallic catalyst with atomically ordered structure and rigorously separated Pt single atoms was fabricated, which showed outstanding robustness in 240 h long-term operation at 600 °C with the deactivation rate constant kd as low as 0.00078 h−1, ranking among the lowest reported values. Based on various in situ characterizations and theoretical calculations, it was proved that the catalyst stability not only resulted from the separated Pt single-atom sites but also significantly affected by the distance of adjacent Pt atoms. An increasing distance to 3.25 Å in the Pt2In3 could induce a weak π-adsorption configuration of propylene on Pt sites, which facilitated the desorption of propylene and restrained the side reactions like coking.

Support Pore Structure and Composition Strongly Influence the Direct Air Capture of CO2 on Supported Amines.

A variety of amine-impregnated porous solid sorbents for direct air capture (DAC) of CO2 have been developed, yet the effect of amine-solid support interactions on the CO2 adsorption behavior is still poorly understood. When tetraethylenepentamine (TEPA) is impregnated on two different supports, commercial γ-Al2O3 and MIL-101(Cr), they show different trends in CO2 sorption when the temperature (-20 to 25 °C) and humidity (0-70% RH) of the simulated air stream are varied. In situ IR spectroscopy is used to probe the mechanism of CO2 sorption on the two supported amine materials, with weak chemisorption (formation of carbamic acid) being the dominant pathway over MIL-101(Cr)-supported TEPA and strong chemisorption (formation of carbamate) occurring over γ-Al2O3-supported TEPA. Formation of both carbamic acid and carbamate species is enhanced over the supported TEPA materials under humid conditions, with the most significant enhancement observed at -20 °C. However, while equilibrium H2O sorption is high at cold temperatures (e.g., -20 °C), the effect of humidity on a practical cyclic DAC process is expected to be minimal due to slow H2O uptake kinetics. This work suggests that the CO2 capture mechanisms of impregnated amines can be controlled by adjusting the degree of amine-solid support interaction and that H2O adsorption behavior is strongly affected by the properties of the support materials. Thus, proper selection of solid support materials for amine impregnation will be important for achieving optimized DAC performance under varied deployment conditions, such as cold (e.g., -20 °C) or ambient temperature (e.g., 25 °C) operations.

Graphitic carbon nitride (g-C3N4) as a super support for Mn–Ce based NH3-SCR catalyst: Improvement of catalytic performance and H2O/SO2 tolerance for NOx removal

Low temperature NH3 selective catalytic reduction (NH3-SCR) technology is an efficient and economical strategy for NOx removal. In this study, Mn–Ce oxides supported on graphitic carbon nitride (g-C3N4) was applied to the NH3-SCR of NOx at low temperature compared with Mn–Ce oxides supported on commercial TiO2, γ-Al2O3, and montmorillonite (MNT). The NOx conversion and H2O/SO2 tolerance of 8% Mn–Ce/g–C3N4–300 were superior to those of 8% Mn–Ce/TiO2-300, 8% Mn–Ce/γ-Al2O3-300 and 8% Mn–Ce/MNT-300 in the temperature window of 100–300 °C, and more than 95% NOx conversion could be obtained within the whole temperature range. According to the experimental and characteriazation results, the superior low temperature NH3-SCR performance of 8% Mn–Ce/g–C3N4–300 could be attributed to the formation of Ce–O–Mn solid solution structure, the higher concentrations of the surface elements, the optimun low-temperature reduction behavior, the largest amount of total acid sites, the highest (Mn4++Mn3+)/(Mn4++Mn3++Mn2+) and (Ce3+)/(Ce3++Ce4+) ratios, and the modest Oα/(Oα+Oβ) ratio.

Distinct morphology-dependent behaviors for Au/γ-Al2O3 catalysts: enhanced thermal stabilization in CO oxidation reaction.

The durability of supported metal catalysts usually suffers from sintering, the metal nanoparticles aggregating into larger sizes and subsequent loss of reactive surface, resulting in catalysts deactivation when heated at elevated temperatures. Herein, we investigate the evolution of Au species on different morphologies of γ-Al2O3 and surprisingly found vastly different behavior for the dispersion of surface Au nanoparticles. A nanorod-shaped γ-Al2O3 is prepared by the hydrothermal method resulting in an extraordinary catalyst support that can stabilize Au nanoparticles at annealing temperatures up to 700 °C. In contrast, the Au-supported catalyst prepared using commercial γ-Al2O3 shows a greater degree of inactivation under the same conditions. Remarkably, the unique morphology of such nanorod-shaped γ-Al2O3 is beneficial in preventing Au nanoparticles from sintering. The γ-Al2O3 nanorods are more effective than the commercial γ-Al2O3 at anchoring the Au nanoparticles. The results of X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and H2-TPR, reveal the interfacial interactions between Au nanoparticles and γ-Al2O3 nanorods, yielding a sinter-stability of the obtained Au/γ-Al2O3 nanorods catalyst. This synthetic strategy is simple and amenable to the large-scale manufacture of thermally stable γ-Al2O3 for industrial applications. Here, we investigate the morphology-dependent behavior of Au nanoparticles dispersed on different morphologies of γ-Al2O3. The result of X-ray photoelectron spectroscopy (XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and H2-TPR, reveal the interfacial interactions between Au nanoparticles and gamma alumina nanorods. Au nanoparticles on γ-Al2O3 nanorods exhibit higher sinter-resistant performance than those on commercial γ-Al2O3.

Complete mechanochemical defluorination of perfluorooctanoic acid using Al2O3 and Al powders through matching electron-mediated reduction with decarboxylation

This work reports a mechanochemical (MC) method for complete defluorination of perfluorooctanoic acid (PFOA) by using Al and Al2O3 as milling agents. Both the Al/Al2O3 molar ratio (nAl/nAl2O3) and the pre-thermal treatment of Al2O3 strongly influenced the defluorination of PFOA. When commercial γ-Al2O3 was pre-treated at 1200 °C, the use of Al and heat-treated γ-Al2O3 with nAl/nAl2O3 of 1: 1 led to PFOA defluorination of 100% after ball milling for 26 min at 350 rpm, being much higher than those (8.3%–58.1%) for using singlet milling agents or binary milling agents containing γ-Al2O3 pre-heated at temperatures lower than 700 °C. It was clarified that the carboxylate-mediated adsorption of PFOA on Al2O3 was essential for the MC decarboxylation as a degradation initiation step, and the in-situ generated electron on milled Al consequently caused the reductive dissociation of C–F bonds in the decarboxylation intermediate. A larger nAl/nAl2O3 increased the in-situ electron generation rate (re), and a higher heat-treatment temperature decreased OH−/H2O adsorbed on Al2O3 to low the PFOA decarboxylation rate (rdec). The re/rdec ratio determined defluorination pathways, and the percentage of the defluorination of PFOA in its total degradation including the generation of any degradation intermediates increased linearly with increasing re/rdec.

Cascade hydrogenation of nitrobenzene to dicyclohexylamine with Pd/γ-Al2O3: The role of acid sites

Direct hydrogenation of nitrobenzene (NB) to dicyclohexylamine (DCHA) is a green but challenging process due to the competition of cross-coupling reaction (to DCHA) and hydrogenation reaction (to byproduct). Herein, we report that the cross-coupling reaction to desired DCHA is greatly enhanced by tuning the acidity of supported Pd catalysts. It was found that Pd NPs loading on commercial γ-Al2O3 (γ-Al2O3-Com) with moderate acidity were more selective than those on neutral SBA-15 or strongly acidic γ-Al2O3 nanorods. The presence of acid site could promote the coupling reaction. By analyzing the correlation between hydrogenation activity and DCHA selectivity, it was found that the matched rate of hydrogenation and cross-coupling is the key factor to achieve high selectivity. This study may open a new avenue for the hydrogenation of nitroarenes to DCHA by regulating the acidity of supports and the reaction conditions.

Disperse alumina nanoparticles prepared by ball milling and acid corrosion

High-yield production of high-purity, disperse, ultrafine, and equiaxed gamma-alumina (γ-Al2O3) nanoparticles with narrow size distributions are essential for their applications. However, the synthesis of γ-Al2O3 nanoparticles by calcination of alumina precursors usually results in severe aggregates. In our present work, commercial γ-Al2O3 particles with an irregular shape, large size, and severe aggregates were directly ball-milled. The milled powders were subsequently corroded with hydrochloric acid to obtain γ-Al2O3 nanoparticles. The γ-Al2O3 nanoparticles obtained are dispersed without aggregates, equiaxed in shape, and ultrafine with a mean particle size of 6.2 nm. The disperse γ-Al2O3 nanoparticles are with high purity (99.994 %, mass per cent) and yield. Then γ-Al2O3 nanoparticles were separated by fractionated coagulation to narrow their size distribution. After coagulation separations, γ-Al2O3 nanoparticles with mean particle sizes of 4.8, 6.6, and 7.7 nm and respective size distributions of 2–9, 2–12, and 2–15 nm were acquired. This high-yield preparation process for γ-Al2O3 nanoparticles is simple and scaled up. Furthermore, using commercial γ-Al2O3 powders as starting material, disperse, and equiaxed α-Al2O3 nanoparticles with a mean particle size of 7.6 nm and purity of 95.98 % (mass per cent) were also prepared by ball milling at a higher ball-to-powder weight ratio of 60:1 and acid corrosion.

An Al2O3-supported NiFe bimetallic catalyst derived from hydrotalcite precursors for efficient CO2 methanation

The unsatisfactory low-temperature activity of Ni based catalysts in CO2 methanation calls for further optimization of catalyst design. In the present work, an efficient Ni7Fe1/Al2O3 bimetallic catalyst was derived from hydrotalcite precursors that were grown in-situ on the commercial γ-Al2O3. The resultant Ni7Fe1/Al2O3 bimetallic catalyst exhibited exceptional low-temperature activity, whose CO2 conversion reached 75.3% at 270 ºC under atmospheric pressure. Moreover, the Ni7Fe1/Al2O3 catalyst remained stable at 350 ºC for 50 h. Structural characterizations revealed that the exceptional activity over the bimetallic catalyst was closely related with the formation of NiFe alloy, which modified the electronic property, enhanced the metal reducibility and enriched the surface basic sites of Ni catalysts. The good stability on the bimetallic catalyst was mainly ascribed to the excellent coke- and sintering- resistance. This work develops an efficient methanation catalyst and clarifies the effect of bimetallic synergism in CO2 methanation.

Sustainable Production of Terephthalonitrile Via in Situ Catalytic Pyrolysis of Pet with Urea Over Commercial Γ-Al2o3

Sustainable Production of Terephthalonitrile Via in Situ Catalytic Pyrolysis of Pet with Urea Over Commercial Γ-Al2o3

Fe-doped Al2O3 nanoplatforms as efficient and recyclable photocatalyst for the dyes remediation

γ-Al2O3 nanowires (NW) were synthetized and impregnated with different amounts of iron (2, 6 and 10 wt%). Catalysts were further characterized by powder X-ray, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, UV–visible diffuse reflectance, temperature-programmed reduction, thermogravimetric analysis, transmission electron microscopy, X-ray photoelectron spectrometry and atomic absorption. The obtained materials were evaluated as heterogeneous photocatalysts in the degradation of azo dye methyl orange as model compound employing a 125 W high-pressure mercury lamp. After 240 min under irradiation the complete decoloration and 69% of mineralization was obtained when Fe6NW was employed. When commercial γ-Al2O3 was employed as support of 6 wt%. of iron and evaluated in photodegradation the final decoloration reached up to only 46%. Reaction parameters such as iron amount, catalyst amount, pH, effect of support and reuses, were evaluated. The photocatalyst was employed for five consecutive reaction cycles with only a 10% of diminish of activity, resulting in an attractive low-cost and benefit in heterogeneous catalysis.

Modification of the properties of γ-alumina as a support for nickel and molybdate catalysts by addition of silica

Commercial pure γ-Al2O3 and SiO2 (1−30 wt.%) doped γ-Al2O3 were characterized as acid catalysts in ethanol conversion and used as supports for NiO and MoO3. Supported catalysts were prepared by incipient wetness impregnation. All catalytic materials were characterized by BET, XRD, FE-SEM microscopy, UV–vis and IR spectroscopies. Pure and silica-doped NiO/Al2O3 materials were used as precursors of metal catalysts for CO2 hydrogenation. Pure and silica-doped MoO3/Al2O3 materials were used as catalysts for ethanol oxidative dehydrogenation to acetaldehyde.These data show that the addition of silica in moderate amounts selectively influences a part of the alumina surface and strongly modifies the dispersing properties of alumina support. In particular, silica preferentially bonds over the strongest Lewis acid-base sites of γ-Al2O3, where also Ni2+ and molybdate species tend to interact. Being the SiO2-Al2O3 interaction stronger than the NiO-Al2O3 interaction and the MoO3-Al2O3 interaction, silica displaces nickel and molybdate species to less preferential sites where their interaction with exposed alumina is weaker. This results in more easily reducible Ni2+ species and larger Ni metal particles for silica doped Ni/Al2O3, and more monomeric and less polymeric molybdate species for silica doped MoO3/Al2O3.

Mesoporous Adsorbents for Desulfurization of Model Diesel Fuel: Optimization, Kinetic, and Thermodynamic Studies

Mesoporous alumina-based adsorbents consisting of a π-electron acceptor complexing agent (2,7-dinitro-9-fluorenone) were synthesized and characterized. Adsorbents were screened for the removal of sulfur compounds from a model ultra-low-sulfur diesel fuel via a charge transfer complex (CTC) mechanism. The sulfur adsorption isotherms and kinetics were examined. The kinetics of sulfur adsorption followed a pseudo-second-order model with the CTC adsorbents. Among the three adsorbents screened, a commercial γ-Al2O3 CTC adsorbent showed the highest desulfurization in a short-run period. The regeneration of spent adsorbent was studied with three different polar solvents, namely chloroform, dichloromethane, and carbon tetrachloride. Dichloromethane was found to be the most suitable solvent for extracting a major portion of sulfur compounds occupied in the pores of the spent adsorbent. γ-Al2O3 CTC adsorbent can be reused after regeneration. Thermodynamic parameters such as Ea, ΔG, ΔH, and ΔS provided a better insight into the adsorption process.

Significant impact of γ-Al2O3 facet structure on the character and performance of surface Co-Mo sulfides for CO removal in H2 fuel via water gas shift

Three morphologically uniform γ-Al2O3 crystallites [Al2O3 hexagonal plates (Al2O3-HP), stacked hexagonal plates (Al2O3-SHP) and rods (Al2O3-R)] were controllably synthesized. The Co-Mo oxide precursor was loaded on these γ-Al2O3 substrates via aqueous incipient wetness impregnation and transformed to the sulfides under 10% H2S/H2 (v/v) atmosphere. The mainly exposed facet of Al2O3-HP and Al2O3-SHP was identified to be the (110) and (100)/(111), respectively; whereas a polycrystalline structure was observed over Al2O3-R. The original structural feature of oxide precursors, i.e., 2D polymeric/monomeric as well as 3D polymeric/MoO3 species substantially varied over Al2O3-HP, Al2O3-SHP, and Al2O3-R, which in turn determines the effectiveness in sulfidation of surface oxide precursors. The richness of MoS2/Co9S8/Co-Mo-S species, and less fraction of partially sulphurated CoMoOxS2 as well as CoOx/SOx2− entities were recognized over Al2O3-HP. Based on the areal activity at 250 °C, the sulfides-Al2O3 (110) interface is approximately 6–13.8 times more active than the poly-crystalline or commercial γ-Al2O3 supported sulfides for water gas shift (WGS) in a hydrogen-rich stream. The sulfides-Al2O3 (110) interface also notably outperformed the sulfides-Al2O3 (100)/(111) interfaces for the reaction.

Preparation of Ni2P Supported on Al2O3 and B2O3 Mixed Oxides by Temperature-Programmed Reduction of Phosphate Precursors with Low P/Ni Ratios

Two types of mixed oxides of B2O3 and Al2O3 were prepared. Aluminum borates (ABx, x represents the B/(B + Al) ratio) were prepared by low-temperature thermal decomposition of aluminum nitrate and H3BO3 sustained by the simultaneous oxidation of an organic agent (glycerol), while B2O3-Al2O3 with B/(B + Al) ratio of 0.3 was obtained by incipient wetness impregnation of H3BO3 on a commercial γ-Al2O3 support. Tetrahedrally, pentahedrally, and octahedrally coordinated Al3+ cations were all present in AB0.3 with ratios of 10.9/21.3/67.8, while no pentahedrally coordinated Al3+ was observed in B2O3-Al2O3. B2O3 was enriched in the surface of AB0.3. The Ni2P phase was obtained by temperature-programmed reduction of a phosphate precursor with a P/Ni ratio as low as 1.2 supported over both AB0.3 (Ni-P(1.2)/AB0.3) and B2O3-Al2O3 (Ni-P(1.2)/B2O3-Al2O3). This suggests that the surface B2O3 inhibits the reaction between nickel phosphates and Al2O3, and thus facilitates the formation of Ni2P. The hydrodesulfurization (HDS) of dibenzothiophene (DBT) over the supported Ni2P catalysts occurred mainly by the direct desulfurization pathway, and Ni-P(1.2)/B2O3-Al2O3 was much more active than Ni-P(1.2)/AB0.3. These features make B2O3-Al2O3 a promising support for Ni2P catalysts. The HDS of DBT followed a pseudo-first-order kinetics over Ni-P(1.2)/B2O3-Al2O3, whereas over Ni-P(1.2)/AB0.3 it can be described by pseudo-zero-order kinetics. The pseudo-zero-order kinetics suggests a strong adsorption of DBT on Ni-P(1.2)/AB0.3, which could be responsible for its lower activity.

Effect of pore texture property of mesoporous alumina on adsorption performance of ammonia gas

We report that the adsorption of ammonia gas on the synthesized mesoporous alumina (MA) with the controlled pore texture properties were measured. The MA adsorbents with controlled pore properties were synthesized by the Evaporation Induced Self Assembly (EISA) method. It was found that the pore size, and surface area could be adjusted by changing the mole ratio of the acid to alumina precursor during the preparation procedure. When the MA materials were used as adsorbents on ammonia gas adsorption, both adsorption kinetics and capacity were highly influenced by the pore texture properties. Pseudo first order that adsorption kinetic constant and the effective diffusivities of alumina adsorbents decreased with decreasing pore size or increasing surface area, while adsorption capacities increased. In order to estimate the adsorption behavior of ammonia gas, the Langmuir, Freundlich, Sips, and Toth isotherm models were employed. Langmuir model-based calculation reveals that mesoporous alumina MA-1.1 adsorbent with a large surface area and a small pore size shows the best performance in terms of the calculated maximum adsorption capacity of ammonia (193.57 mg/g), which is almost double that of other MA adsorbents (MA-3.3, MA-4.4) and 2.89 times that of commercial γ-Al2O3.

Recovery of pentoses-containing olive stones for their conversion into furfural in the presence of solid acid catalysts

Olive stones were employed as feedstock for furfural production in two stages: 1) autohydrolysis of hemicellulosic fraction to recover their pentoses, mainly xylose, and 2) subsequent dehydration of pentoses into furfural. Autohydrolysis step was optimized by using different experimental conditions (temperature: 160−200 °C and time: 30−75 min), giving rise to liquors with different xylose concentrations, since hydrolysis was incomplete in some cases. The combined use of a commercial γ-Al2O3 and CaCl2 led to total hydrolysis of non-hydrolyzed pentosans after autohydrolysis step, and the subsequent dehydration of pentoses into furfural. The maximum values of furfural yield and efficiency were 23 and 96 %, respectively, after only 60 min at 150 °C by using liquor obtained by autohydrolysis at 180 °C and 30 min (L5.1) as source of pentoses. This liquor, L5.1, provided better catalytic results than other liquors which had shown higher xylose concentration after autohydrolysis, probably due to these latter also exhibited a higher concentration of organic acids; thus, the presence of organic acids, such as acetic and lactic acids, could promote undesired reactions leading to lower furfural yields. Finally, γ-Al2O3 was more effective for furfural production under these experimental conditions than other solid acid catalysts, such as mesoporous Nb2O5, Nb-doped SBA-15 and Zr-doped HMS silicas, probably due to alumina has a higher density of acid sites.